footnotes/class/task.php

<?php
/**
 * Includes the core function of the Plugin - Search and Replace the Footnotes.
 *
 * @filesource
 * @author Stefan Herndler
 * @since 1.5.0
 *
 *
 * @lastmodified  2021-02-12T1641+0100
 *
 * @since 2.0.0  Bugfix: various.
 * @since 2.0.4  Bugfix: Referrers and backlinks: remove hard links to streamline browsing history, thanks to @theroninjedi47 bug report.
 * @since 2.0.5  Bugfix: Reference container: fix relative position through priority level, thanks to @june01 @imeson @spaceling bug reports, thanks to @spaceling code contribution.
 * @since 2.0.5  Update: Hooks: Default-enable all hooks to prevent footnotes from seeming broken in some parts.
 * @since 2.0.6  Bugfix: Infinite scroll: debug autoload by adding post ID, thanks to @docteurfitness code contribution.
 * @since 2.0.6  Bugfix: Priority level back to PHP_INT_MAX (ref container positioning not this plugin’s responsibility).
 * @since 2.0.6  Bugfix: Reference container: fix line breaking behavior in footnote number clusters.
 * @since 2.0.7  BUGFIX: Hooks: Default-disable 'the_post', thanks to @spaceling @@markcheret @nyamachi @whichgodsaves @spiralofhope2 @mmallett @andreasra @widecast @ymorin007 @tashi1es bug reports.
 * @since 2.0.9  Bugfix: Remove the_post hook  2020-11-08T1839+0100.
 * @since 2.1.0  Adding: Tooltips: Read-on button: Label: configurable instead of localizable, thanks to @rovanov example provision.
 * @since 2.1.1  Bugfix: Referrers, reference container: Combining identical footnotes: fix dead links and ensure referrer-backlink bijectivity, thanks to @happyches bug report.
 * @since 2.1.1  Bugfix: Reference container: fix start pages by making its display optional, thanks to @dragon013 bug report.
 * @since 2.1.1  Bugfix: Referrers: new setting for vertical align: superscript (default) or baseline (optional), thanks to @cwbayer bug report.
 * @since 2.1.1  Bugfix: Reference container: option to append symbol (prepended by default), thanks to @spaceling code contribution.
 * @since 2.1.1  Bugfix: Reference container: Backlink symbol: make optional, not suggest configuring it to invisible, thanks to @spaceling feedback.
 * @since 2.1.1  Bugfix: Dashboard: priority level setting for the_content hook, thanks to @imeson bug report.
 * @since 2.1.1  Bugfix: Tooltips: optional alternative JS implementation with CSS transitions to fix configuration-related outage, thanks to @andreasra feedback.
 * @since 2.1.1  Bugfix: Reference container: option to restore pre-2.0.0 layout with the backlink symbol in an extra column.
 * @since 2.1.2  Bugfix: Dashboard: priority level settings for all other hooks, thanks to @nikelaos bug report.
 * @since 2.1.3  Bugfix: Reference container: fix width in mobile view by URL wrapping for Unicode-non-conformant browsers, thanks to @karolszakiel bug report.
 * @since 2.1.4  Bugfix: Styling: Referrers and backlinks: make link elements optional to fix issues.
 * @since 2.1.4  Bugfix: Reference container: Backlink symbol: support for appending when combining identicals is on.
 * @since 2.1.4  Bugfix: Reference container: make separating and terminating punctuation optional and configurable, thanks to @docteurfitness issue report and code contribution.
 * @since 2.1.4  Bugfix: Reference container: Backlinks: fix stacked enumerations by adding optional line breaks.
 * @since 2.1.4  Bugfix: Reference container: fix layout issues by moving backlink column width to settings.
 * @since 2.1.4  Bugfix: Styling: Tooltips: fix font size issue by adding font size to settings with legacy as default.
 * @since 2.1.4  Bugfix: Scroll offset: make configurable to fix site-dependent issues related to fixed headers.
 * @since 2.1.4  Bugfix: Scroll duration: make configurable to conform to website content and style requirements.
 * @since 2.1.4  Bugfix: Tooltips: make display delays and fade durations configurable to conform to website style.
 * @since 2.1.4  Bugfix: Referrers and backlinks: Styling: make link elements optional to fix issues, thanks to @docteurfitness issue report and code contribution.
 * @since 2.1.4  Bugfix: Reference container, tooltips: fix line wrapping of URLs (hyperlinked or not) based on pattern, not link element.
 * @since 2.1.4  Bugfix: Reference container: Backlink symbol: support for appending when combining identicals is on.
 * @since 2.1.4  Bugfix: Reference container: Backlinks: fix line breaking with respect to separators and terminators.
 * @since 2.1.5  Bugfix: Reference container, tooltips: URL wrap: exclude image source too, thanks to @bjrnet21 bug report.
 * @since 2.1.6  Bugfix: Reference container, tooltips: URL wrap: fix regex, thanks to @a223123131 bug report.
 * @since 2.1.6  Bugfix: Dashboard: URL wrap: add option to properly enable/disable URL wrap.
 * @since 2.2.0  Adding: Reference container: support for custom position shortcode, thanks to @hamshe issue report.
 * @since 2.2.3  Bugfix: Custom CSS: insert new CSS in the public page header element after existing CSS.
 * @since 2.2.5  Bugfix: Reference container: delete position shortcode if unused because position may be widget or footer, thanks to @hamshe bug report.
 * @since 2.2.5  Bugfix: Reference container: Label: make bottom border an option, thanks to @markhillyer issue report.
 * @since 2.2.5  Bugfix: Reference container: Label: option to select paragraph or heading element, thanks to @markhillyer issue report.
 * @since 2.2.5  Update: Tooltips: Alternative tooltips: connect to position/timing settings (for themes not supporting jQuery tooltips).
 * @since 2.2.6  Bugfix: Reference container, tooltips: URL wrap: make the quotation mark optional wrt query parameters, thanks to @spiralofhope2 bug report.
 * @since 2.2.7  Bugfix: Reference container, tooltips: URL wrap: remove a bug introduced in the regex, thanks to @rjl20 @spaceling @lukashuggenberg @klusik @friedrichnorth @bernardzit bug reports.
 * @since 2.2.8  Bugfix: Reference container, tooltips: URL wrap: correctly make the quotation mark optional wrt query parameters, thanks to @spiralofhope2 bug report.
 * @since 2.2.9  Bugfix: Reference container, tooltips: URL wrap: account for RFC 2396 allowed characters in parameter names.
 * @since 2.2.9  Bugfix: Reference container, widget_text hook: support for multiple containers in a page, thanks to @justbecuz bug report.
 * @since 2.2.9  Bugfix: Reference container, tooltips: URL wrap: exclude URLs also where the equals sign is preceded by an entity or character reference.
 * @since 2.2.10 Bugfix: Reference container: add option for table borders to restore pre-2.0.0 design, thanks to @noobishh issue report.
 * @since 2.2.10 Bugfix: Reference container, tooltips: URL wrap: support also file transfer protocol URLs.
 * @since 2.3.0  Bugfix: Reference container: convert top padding to margin and make it a setting, thanks to @hamshe bug report.
 * @since 2.3.0  Adding: Referrers and backlinks: optional hard links for AMP compatibility, thanks to @psykonevro bug report, thanks to @martinneumannat code contribution.
 * @since 2.3.0  Bugfix: Dashboard: Custom CSS: swap migration Boolean, meaning 'show legacy' instead of 'migration complete', due to storage data structure constraints.
 * @since 2.4.0  Adding: Footnote delimiters: syntax validation for balanced footnote start and end tag short codes.
 * @since 2.4.0  Bugfix: Scroll offset: initialize to safer one third window height for more robustness, thanks to @lukashuggenberg bug report.
 * @since 2.4.0  Bugfix: Reference container: Label: set empty label to U+202F NNBSP for more robustness, thanks to @lukashuggenberg feedback.
 * @since 2.4.0  Bugfix: Templates: optimize template load and processing based on settings, thanks to @misfist code contribution.
 * @since 2.4.0  Bugfix: Process: initialize hard link address variables to empty string to fix 'undefined variable' bug, thanks to @a223123131 bug report.
 * @since 2.5.0  Bugfix: Hooks: support footnotes on category pages, thanks to @vitaefit bug report, thanks to @misfist code contribution.
 * @since 2.5.0  Bugfix: Footnote delimiters: Syntax validation: exclude certain cases involving scripts, thanks to @andreasra bug report.
 * @since 2.5.0  Bugfix: Footnote delimiters: Syntax validation: complete message with hint about setting, thanks to @andreasra bug report.
 * @since 2.5.0  Bugfix: Footnote delimiters: Syntax validation: limit length of quoted string to 300 characters, thanks to @andreasra bug report.
 * @since 2.5.1  Bugfix: Hooks: support footnotes in Popup Maker popups, thanks to @squatcher bug report.
 * @since 2.5.2  Update: Tooltips: ability to display dedicated content before `[[/tooltip]]`, thanks to @jbj2199 issue report.
 * @since 2.5.3  Bugfix: Reference container, tooltips: URL wrap: exclude URL pattern as folder name in Wayback Machine URL, thanks to @rumperuu bug report.
 * @since 2.5.4  Bugfix: Referrers: optional fixes to vertical alignment, font size and position (static) for in-theme consistency and cross-theme stability, thanks to
 * @since 2.5.4  Bugfix: Reference container, tooltips: URL wrap: account for leading space in value, thanks to @karolszakiel example provision.
 * @since 2.5.4  Update: Reference container: Hard backlinks (optional): optional configurable tooltip hinting to use the backbutton instead, thanks to @@theroninjedi47 bug report.
 * @since 2.5.4  Bugfix: Tooltips: fix display in Popup Maker popups by correcting a coding error.
 */

// If called directly, abort:
defined( 'ABSPATH' ) or die;

/**
 * Searches and replaces the footnotes.
 * Generates the reference container.
 *
 * @author Stefan Herndler
 * @since 1.5.0
 */
class MCI_Footnotes_Task {

    /**
     *        PROPERTIES
     */

    /**
     * Contains all footnotes found on current public page.
     *
     * @author Stefan Herndler
     * @since 1.5.0
     * @var array
     */
    public static $a_arr_Footnotes = array();

    /**
     * Flag if the display of 'LOVE FOOTNOTES' is allowed on the current public page.
     *
     * @author Stefan Herndler
     * @since 1.5.0
     * @var bool
     */
    public static $a_bool_AllowLoveMe = true;

    /**
     * Prefix for the Footnote html element ID.
     *
     * @author Stefan Herndler
     * @since 1.5.8
     * @var string
     */
    public static $a_str_Prefix = "";

    /**
     * Infinite scroll / autoload or archive view
     *
     * - Bugfix: Infinite scroll: debug autoload by adding post ID, thanks to @docteurfitness code contribution
     *
     * @since 2.0.6
     * @var int
     *
     * @contributor @docteurfitness
     * @link https://wordpress.org/support/topic/auto-load-post-compatibility-update/#post-13618833
     *
     * @reporter @docteurfitness
     * @link https://wordpress.org/support/topic/auto-load-post-compatibility-update/
     *
     * As multiple posts are appended to each other, functions and fragment IDs must be disambiguated.
     * post ID to make everything unique wrt infinite scroll and archive view:
     */
    public static $a_int_PostId = 0;

    /**
     * Multiple reference containers in content and widgets
     *
     * - Bugfix: Reference container, widget_text hook: support for multiple containers in a page, thanks to @justbecuz bug report.
     *
     * @since 2.2.9
     * @datetime 2020-12-25T0338+0100
     *
     * @reporter @justbecuz
     * @link https://wordpress.org/support/topic/reset-footnotes-to-1/
     * @link https://wordpress.org/support/topic/reset-footnotes-to-1/#post-13662830
     *
     * @var int 1; incremented each time after a reference container is inserted
     *
     * This ID disambiguates multiple reference containers in a page
     * as they may occur when the widget_text hook is active and the page
     * is built with Elementor and has an accordion or similar toggle sections.
     */
    public static $a_int_ReferenceContainerId = 1;

    /**
     * Template process optimization
     *
     * - Bugfix: Templates: optimize template load and processing based on settings, thanks to @misfist code contribution.
     *
     * @since 2.4.0
     * @datetime 2021-01-04T1355+0100
     *
     * @author Patrizia Lutz @misfist
     *
     * @link https://wordpress.org/support/topic/template-override-filter/#post-13864301
     * @link https://github.com/misfist/footnotes/releases/tag/2.4.0d3 repository
     * @link https://github.com/misfist/footnotes/compare/2.4.0%E2%80%A62.4.0d3 diff
     *
     * @var bool
     *
     * Streamline process depending on tooltip enabled status.
     * Load tooltip inline script only if jQuery tooltips are enabled.
     * Actual value depends on settings.
     */
    public static $a_bool_TooltipsEnabled = false;
    public static $a_bool_AlternativeTooltipsEnabled = false;

    /**
     * Hard links for AMP compatibility
     *
     * @since 2.0.0  Bugfix: footnote links script independent.
     *
     *
     * - Bugfix: Referrers and backlinks: remove hard links to streamline browsing history, thanks to @theroninjedi47 bug report.
     *
     * @since 2.0.4
     *
     * @reporter @theroninjedi47
     * @link https://wordpress.org/support/topic/hyperlinked-footnotes-creating-excessive-back-history/
     *
     *
     * - Adding: Referrers and backlinks: optional hard links for AMP compatibility, thanks to @psykonevro bug report, thanks to @martinneumannat code contribution.
     *
     * @since 2.3.0
     * @var bool|str|int
     *
     * @contributor @martinneumannat
     * @link https://wordpress.org/support/topic/making-it-amp-compatible/
     *
     * @reporter @psykonevro
     * @link https://wordpress.org/support/topic/footnotes-is-not-amp-compatible/
     *
     * The official AMP plugin strips off JavaScript, breaking Footnotes’
     * animated scrolling.
     */
    public static $a_bool_HardLinksEnable        = false;
    public static $a_str_ReferrerLinkSlug        = 'r';
    public static $a_str_FootnoteLinkSlug        = 'f';
    public static $a_str_LinkIdsSeparator        = '+';
    public static $a_str_PostContainerIdCompound = '';

    /**
     * Scroll offset
     *
     * - Bugfix: Scroll offset: make configurable to fix site-dependent issues related to fixed headers.
     *
     * @since 2.1.4
     * @datetime 2020-12-05T0538+0100
     *
     *
     * - Bugfix: Scroll offset: initialize to safer one third window height for more robustness, thanks to @lukashuggenberg bug report.
     *
     * @since 2.4.0
     * @datetime 2021-01-03T2055+0100
     * @datetime 2021-01-04T0504+0100
     *
     * @reporter @lukashuggenberg
     * @link https://wordpress.org/support/topic/2-2-6-breaks-all-footnotes/#post-13857922
     *
     * @var int
     *
     * Websites may use high fixed headers not contracting at scroll.
     * Scroll offset may now need to get into inline CSS.
     * Hence it needs to be loaded twice, because priority levels may not match.
     */
    public static $a_int_ScrollOffset            = 34;

    /**
     * Optional link element for footnote referrers and backlinks
     *
     * @since 2.0.0  add link elements along with hard links.
     *
     *
     * - Bugfix: Referrers and backlinks: Styling: make link elements optional to fix issues, thanks to @docteurfitness issue report and code contribution.
     *
     * @since 2.1.4
     * @datetime 2020-11-25T1306+0100
     * @datetime 2020-11-26T1051+0100
     *
     * @contributor @docteurfitness
     * @link https://wordpress.org/support/topic/update-2-1-3/#post-13704194
     *
     * @reporter @docteurfitness
     * @link https://wordpress.org/support/topic/update-2-1-3/
     *
     *
     * - Adding: Referrers and backlinks: optional hard links for AMP compatibility, thanks to @psykonevro bug report, thanks to @martinneumannat code contribution.
     *
     * @since 2.3.0
     * @datetime 2020-12-30T2313+0100
     *
     * @contributor @martinneumannat
     * @link https://wordpress.org/support/topic/making-it-amp-compatible/
     *
     * @reporter @psykonevro
     * @link https://wordpress.org/support/topic/footnotes-is-not-amp-compatible/
     *
     * Although widely used for that purpose, hyperlinks are disliked for footnote linking.
     * Browsers may need to be prevented from logging these clicks in the browsing history,
     * as logging compromises the usability of the 'return to previous' button in browsers.
     * For that purpose, and for scroll animation, this linking is performed by JavaScript.
     *
     * Link elements raise concerns, so that mitigating their proliferation may be desired.
     *
     * By contrast, due to an insufficiency in the CSS standard, coloring elements with the
     * theme’s link color requires real link elements and cannot be done with named colors,
     * as CSS does not support 'color: link|hover|active|visited', after the pseudo-classes
     * of the link element.
     *
     * Yet styling these elements with the link color is not universally preferred, so that
     * the very presence of these link elements may need to be avoided.
     *
     * @see self::$a_bool_HardLinksEnable
     */
    public static $a_str_LinkSpan     = 'span';
    public static $a_str_LinkOpenTag  = '';
    public static $a_str_LinkCloseTag = '';

    /**
     * Dedicated tooltip text
     *
     * - Update: Tooltips: ability to display dedicated content before `[[/tooltip]]`, thanks to @jbj2199 issue report.
     *
     * @since 2.5.2
     * @datetime 2021-01-19T2223+0100
     *
     * @reporter @jbj2199
     * @link https://wordpress.org/support/topic/change-tooltip-text/
     *
     * Tooltips can display another content than the footnote entry
     * in the reference container. The trigger is a shortcode in
     * the footnote text separating the tooltip text from the note.
     * That is consistent with what WordPress does for excerpts.
     */
    public static $a_bool_MirrorTooltipText = false;
    public static $a_str_TooltipShortcode = '[[/tooltip]]';
    public static $a_int_TooltipShortcodeLength = 12;

    /**
     * Footnote delimiter syntax validation
     *
     * - Adding: Footnote delimiters: syntax validation for balanced footnote start and end tag short codes.
     *
     * @since 2.4.0
     * @datetime 2021-01-01T0227+0100
     *
     * @var bool
     *
     * The algorithm first checks for balanced footnote opening and closing tag short codes.
     * The first encountered error triggers the display of a warning below the post title.
     *
     * Unbalanced short codes have caused significant trouble because they are hard to detect.
     * Any compiler or other tool reports syntax errors in the first place. Footnotes’ exception
     * is considered a design flaw, and the feature is released as a bug fix after overdue 2.3.0
     * released in urgency to provide AMP compat before 2021.
     */
    public static $a_bool_SyntaxErrorFlag = true;



    /**
     *        METHODS
     */

    /**
     * Register WordPress Hooks to replace Footnotes in the content of a public page.
     *
     * @author Stefan Herndler
     * @since 1.5.0
     *
     * @since 1.5.4  Adding: Hooks: support 'the_post' in response to user request for custom post types.
     * @since 2.0.5  Bugfix: Reference container: fix relative position through priority level, thanks to @june01 @imeson @spaceling bug reports, thanks to @spaceling code contribution.
     * @since 2.0.5  Update: Hooks: Default-enable all hooks to prevent footnotes from seeming broken in some parts.
     * @since 2.0.6  Bugfix: Priority level back to PHP_INT_MAX (ref container positioning not this plugin’s responsibility).
     * @since 2.0.7  BUGFIX: Hooks: Default-disable 'the_post', thanks to @spaceling @@markcheret @nyamachi @whichgodsaves @spiralofhope2 @mmallett @andreasra @widecast @ymorin007 @tashi1es bug reports.
     * @since 2.0.7  Bugfix: Set priority level back to 10 assuming it is unproblematic  2020-11-06T1344+0100.
     * @since 2.0.8  Bugfix: Priority level back to PHP_INT_MAX (need to get in touch with other plugins).
     * @since 2.1.0  UPDATE: Hooks: remove 'the_post', the plugin stops supporting this hook.
     * @since 2.1.1  Bugfix: Dashboard: priority level setting for the_content hook, thanks to @imeson bug report.
     * @since 2.1.2  Bugfix: Dashboard: priority level settings for all other hooks, thanks to @nikelaos bug report.
     * @since 2.5.0  Bugfix: Hooks: support footnotes on category pages, thanks to @vitaefit bug report, thanks to @misfist code contribution.
     * @since 2.5.1  Bugfix: Hooks: support footnotes in Popup Maker popups, thanks to @squatcher bug report.
     */
    public function registerHooks() {

        /**
         * Priority levels
         *
         * - Bugfix: Reference container: fix relative position through priority level, thanks to @june01 @imeson @spaceling bug reports, thanks to @spaceling code contribution.
         *
         * @since 2.0.5
         * @datetime 2020-11-02T0330+0100
         * @link https://codex.wordpress.org/Plugin_API/#Hook_in_your_Filter
         *
         * @contributor @spaceling
         * @link https://wordpress.org/support/topic/change-the-position-5/#post-13608594
         *
         * @reporter @june01
         * @link https://wordpress.org/support/topic/change-the-position-5/
         *
         * @reporter @imeson
         * @link https://wordpress.org/support/topic/change-the-position-5/#post-13538345
         *
         *
         * - Bugfix: Dashboard: priority level setting for the_content hook, thanks to @imeson bug report.
         *
         * @since 2.1.1
         * @datetime 2020-11-17T0254+0100
         *
         * @reporter @imeson
         * @link https://wordpress.org/support/topic/change-the-position-5/#post-13538345
         *
         *
         * - Bugfix: Dashboard: priority level settings for all other hooks, thanks to @nikelaos bug report.
         *
         * @since 2.1.2
         * @datetime 2020-11-19T1849+0100
         *
         * @reporter @nikelaos
         * @link https://wordpress.org/support/topic/doesnt-work-any-more-11/#post-13676705
         *
         *
         * Setting the_content priority to 10 instead of PHP_INT_MAX i.e. 9223372036854775807
         * makes the footnotes reference container display beneath the post and above other
         * features added by other plugins, e.g. related post lists and social buttons.
         *
         * For YARPP to display related posts below the Footnotes reference container,
         * priority needs to be at least 1200 (i.e. 0 =< $l_int_TheContentPriority =< 1200).
         *
         * PHP_INT_MAX cannot be reset by leaving the number box empty. because browsers
         * (WebKit) don’t allow it, so we must resort to -1.
         * @link https://github.com/Modernizr/Modernizr/issues/171
         */

        // get values from settings:
        $l_int_TheTitlePriority    = intval(MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_INT_EXPERT_LOOKUP_THE_TITLE_PRIORITY_LEVEL));
        $l_int_TheContentPriority  = intval(MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_INT_EXPERT_LOOKUP_THE_CONTENT_PRIORITY_LEVEL));
        $l_int_TheExcerptPriority  = intval(MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_INT_EXPERT_LOOKUP_THE_EXCERPT_PRIORITY_LEVEL));
        $l_int_WidgetTitlePriority = intval(MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_INT_EXPERT_LOOKUP_WIDGET_TITLE_PRIORITY_LEVEL));
        $l_int_WidgetTextPriority  = intval(MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_INT_EXPERT_LOOKUP_WIDGET_TEXT_PRIORITY_LEVEL));

        // PHP_INT_MAX can be set by -1:
        $l_int_TheTitlePriority    = ($l_int_TheTitlePriority    == -1) ? PHP_INT_MAX : $l_int_TheTitlePriority   ;
        $l_int_TheContentPriority  = ($l_int_TheContentPriority  == -1) ? PHP_INT_MAX : $l_int_TheContentPriority ;
        $l_int_TheExcerptPriority  = ($l_int_TheExcerptPriority  == -1) ? PHP_INT_MAX : $l_int_TheExcerptPriority ;
        $l_int_WidgetTitlePriority = ($l_int_WidgetTitlePriority == -1) ? PHP_INT_MAX : $l_int_WidgetTitlePriority;
        $l_int_WidgetTextPriority  = ($l_int_WidgetTextPriority  == -1) ? PHP_INT_MAX : $l_int_WidgetTextPriority ;


        // append custom css to the header
        add_filter('wp_head', array($this, "wp_head"), PHP_INT_MAX);

        // append the love and share me slug to the footer
        add_filter('wp_footer', array($this, "wp_footer"), PHP_INT_MAX);

        if (MCI_Footnotes_Convert::toBool(MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_BOOL_EXPERT_LOOKUP_THE_TITLE))) {
            add_filter('the_title', array($this, "the_title"), $l_int_TheTitlePriority);
        }

        // configurable priority level for reference container relative positioning; default 98:
        if (MCI_Footnotes_Convert::toBool(MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_BOOL_EXPERT_LOOKUP_THE_CONTENT))) {
            add_filter('the_content', array($this, "the_content"), $l_int_TheContentPriority);

            /**
             * Hook for category pages
             *
             * - Bugfix: Hooks: support footnotes on category pages, thanks to @vitaefit bug report, thanks to @misfist code contribution.
             *
             * @since 2.5.0
             * @datetime 2021-01-05T1402+0100
             *
             * @contributor @misfist
             * @link https://wordpress.org/support/topic/footnote-doesntwork-on-category-page/#post-13864859
             *
             * @reporter @vitaefit
             * @link https://wordpress.org/support/topic/footnote-doesntwork-on-category-page/
             *
             * Category pages can have rich HTML content in a term description with article status.
             * For this to happen, WordPress’ built-in partial HTML blocker needs to be disabled.
             * @link https://docs.woocommerce.com/document/allow-html-in-term-category-tag-descriptions/
             */
            add_filter('term_description', array($this, "the_content"), $l_int_TheContentPriority);

            /**
             * Hook for popup maker popups
             *
             * - Bugfix: Hooks: support footnotes in Popup Maker popups, thanks to @squatcher bug report.
             *
             * @since 2.5.1
             * @datetime 2021-01-18T2038+0100
             *
             * @reporter @squatcher
             * @link https://wordpress.org/support/topic/footnotes-use-in-popup-maker/
             */
            add_filter('pum_popup_content', array($this, "the_content"), $l_int_TheContentPriority);
        }

        if (MCI_Footnotes_Convert::toBool(MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_BOOL_EXPERT_LOOKUP_THE_EXCERPT))) {
             add_filter('the_excerpt', array($this, "the_excerpt"), $l_int_TheExcerptPriority);
        }
        if (MCI_Footnotes_Convert::toBool(MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_BOOL_EXPERT_LOOKUP_WIDGET_TITLE))) {
            add_filter('widget_title', array($this, "widget_title"), $l_int_WidgetTitlePriority);
        }
        if (MCI_Footnotes_Convert::toBool(MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_BOOL_EXPERT_LOOKUP_WIDGET_TEXT))) {
            add_filter('widget_text', array($this, "widget_text"), $l_int_WidgetTextPriority);
        }


        /**
         * The the_post hook
         *
         * - Adding: Hooks: support 'the_post' in response to user request for custom post types.
         *
         * @since 1.5.4
         * @accountable @aricura
         * @link https://wordpress.org/support/topic/doesnt-work-in-custon-post-types/#post-5339110
         *
         *
         * - Update: Hooks: Default-enable all hooks to prevent footnotes from seeming broken in some parts.
         *
         * @since 2.0.5
         * @accountable @pewgeuges
         *
         *
         * - BUGFIX: Hooks: Default-disable 'the_post', thanks to @spaceling @@markcheret @nyamachi @whichgodsaves @spiralofhope2 @mmallett @andreasra @widecast @ymorin007 @tashi1es bug reports.
         *
         * @since 2.0.7
         * @accountable @pewgeuges
         * @link https://wordpress.org/support/topic/change-the-position-5/page/2/#post-13630114
         * @link https://wordpress.org/support/topic/footnotes-appearing-in-header/#post-13630303
         * @link https://wordpress.org/support/topic/footnotes-appearing-in-header/page/2/#post-13630799
         * @link https://wordpress.org/support/topic/no-footnotes-anymore/#post-13813233
         *
         * @reporter @spaceling
         * @link https://wordpress.org/support/topic/change-the-position-5/#post-13612697
         *
         * @reporter @markcheret on behalf of W. Beinert
         * @link https://wordpress.org/support/topic/footnotes-now-appear-in-summaries-even-though-this-is-marked-no/
         *
         * @reporter @nyamachi
         * @link https://wordpress.org/support/topic/footnotes-appearing-in-header/
         *
         * @reporter @whichgodsaves
         * @link https://wordpress.org/support/topic/footnotes-appearing-in-header/#post-13622694
         *
         * @reporter @spiralofhope2
         * @link https://wordpress.org/support/topic/2-0-5-broken/
         *
         * @reporter @mmallett
         * @link https://wordpress.org/support/topic/2-0-5-broken/#post-13623208
         *
         * @reporter @andreasra
         * @link https://wordpress.org/support/topic/footnotes-appearing-in-header/#post-13624091
         *
         * @reporter @widecast
         * @link https://wordpress.org/support/topic/2-0-5-broken/#post-13626222
         *
         * @reporter @ymorin007
         * @link https://wordpress.org/support/topic/footnotes-appearing-in-header/#post-13627050
         *
         * @reporter @markcheret on behalf of L. Smith
         * @link https://wordpress.org/support/topic/footnotes-appear-in-random-places-on-academic-website/
         *
         * @reporter @tashi1es
         * @link https://wordpress.org/support/topic/footnotes-appear-in-random-places-on-academic-website/#post-13630495
         *
         *
         * - UPDATE: Hooks: remove 'the_post', the plugin stops supporting this hook.
         *
         * @since 2.1.0
         * @datetime 2020-11-08T1839+0100
         * @accountable @pewgeuges
         */

        // reset stored footnotes when displaying the header
        self::$a_arr_Footnotes = array();
        self::$a_bool_AllowLoveMe = true;
    }

    /**
     * Outputs the custom css to the header of the public page.
     *
     * @author Stefan Herndler
     * @since 1.5.0
     *
     *
     * @since 2.1.1  Bugfix: Reference container: fix start pages by making its display optional, thanks to @dragon013 bug report.
     * @since 2.1.1  Bugfix: Tooltips: optional alternative JS implementation with CSS transitions to fix configuration-related outage, thanks to @andreasra feedback.
     * @since 2.1.3  raise settings priority to override theme style sheets
     * @since 2.1.4  Bugfix: Tooltips: Styling: fix font size issue by adding font size to settings with legacy as default.
     * @since 2.1.4  Bugfix: Reference container: fix layout issues by moving backlink column width to settings.
     * @since 2.2.5  Bugfix: Reference container: Label: make bottom border an option, thanks to @markhillyer issue report.
     * @since 2.2.5  Bugfix: Reference container: Label: option to select paragraph or heading element, thanks to @markhillyer issue report.
     * @since 2.3.0  Bugfix: Reference container: convert top padding to margin and make it a setting, thanks to @hamshe bug report.
     * @since 2.5.4  Bugfix: Referrers: optional fixes to vertical alignment, font size and position (static) for in-theme consistency and cross-theme stability, thanks to @tomturowski bug report.
     */
    public function wp_head() {

        // insert start tag without switching out of PHP:
        echo "\r\n<style type=\"text/css\" media=\"all\">\r\n";

        /**
         * Normalizes the referrers’ vertical alignment and font size.
         *
         * - Bugfix: Referrers: optional fixes to vertical alignment, font size and position (static) for in-theme consistency and cross-theme stability, thanks to @tomturowski bug report.
         *
         * @since 2.5.4
         * @datetime 2021-02-12T1631+0100
         *
         * @reporter @tomturowski
         * @link https://wordpress.org/support/topic/in-line-superscript-ref-rides-to-high/
         *
         * Cannot be included in external style sheet, as it is only optional.
         * The scope is variable too: referrers only, or all superscript elements.
         */
        $l_str_NormalizeSuperscript = MCI_Footnotes_Settings::instance()->get( MCI_Footnotes_Settings::C_STR_FOOTNOTE_REFERRERS_NORMAL_SUPERSCRIPT );
        if ( $l_str_NormalizeSuperscript !== 'no' ) {
            if ( $l_str_NormalizeSuperscript === 'all' ) {
                echo "sup {";
            } else {
                echo ".footnote_plugin_tooltip_text {";
            }
            echo "vertical-align: super; font-size: smaller; position: static;}\r\n";
        }

        /**
         * Reference container display on home page
         *
         * - Bugfix: Reference container: fix start pages by making its display optional, thanks to @dragon013 bug report.
         *
         * @since 2.1.1
         *
         * @reporter @dragon013
         * @link https://wordpress.org/support/topic/possible-to-hide-it-from-start-page/
         */
        if (!MCI_Footnotes_Convert::toBool(MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_BOOL_REFERENCE_CONTAINER_START_PAGE_ENABLE))) {
            echo ".home .footnotes_reference_container { display: none; }\r\n";
        }

        /**
         * Reference container top and bottom margins
         *
         * - Bugfix: Reference container: convert top padding to margin and make it a setting, thanks to @hamshe bug report.
         *
         * @since 2.3.0
         *
         * @reporter @hamshe
         * @link https://wordpress.org/support/topic/reference-container-in-elementor/#post-13786635
         */
        $l_int_ReferenceContainerTopMargin = intval(MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_INT_REFERENCE_CONTAINER_TOP_MARGIN));
        $l_int_ReferenceContainerBottomMargin = intval(MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_INT_REFERENCE_CONTAINER_BOTTOM_MARGIN));
        echo ".footnotes_reference_container {margin-top: ";
        echo empty($l_int_ReferenceContainerTopMargin) ? '0' : $l_int_ReferenceContainerTopMargin;
        echo "px !important; margin-bottom: ";
        echo empty($l_int_ReferenceContainerBottomMargin) ? '0' : $l_int_ReferenceContainerBottomMargin;
        echo "px !important;}\r\n";

        /**
         * Reference container label bottom border
         *
         * - Bugfix: Reference container: Label: make bottom border an option, thanks to @markhillyer issue report.
         * - Bugfix: Reference container: Label: option to select paragraph or heading element, thanks to @markhillyer issue report.
         *
         * @since 2.2.5
         * @datetime 2020-12-18T1447+0100
         *
         * @reporter @markhillyer
         * @link https://wordpress.org/support/topic/how-do-i-eliminate-the-horizontal-line-beneath-the-reference-container-heading/
         *
         */
        if (MCI_Footnotes_Convert::toBool(MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_BOOL_REFERENCE_CONTAINER_LABEL_BOTTOM_BORDER))) {
            echo ".footnote_container_prepare > ";
            echo MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_STR_REFERENCE_CONTAINER_LABEL_ELEMENT);
            echo " {border-bottom: 1px solid #aaaaaa !important;}\r\n";
        }

        /**
         * Reference container table row borders
         *
         * - Bugfix: Reference container: add option for table borders to restore pre-2.0.0 design, thanks to @noobishh issue report.
         *
         * @since 2.2.10
         * @datetime 2020-12-25T2304+0100
         *
         * @reporter @noobishh
         * @link https://wordpress.org/support/topic/borders-25/
         */
        if ( MCI_Footnotes_Convert::toBool(MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_BOOL_REFERENCE_CONTAINER_ROW_BORDERS_ENABLE))) {
            echo ".footnotes_table, .footnotes_plugin_reference_row {";
            echo "border: 1px solid #060606;";
            echo " !important;}\r\n";
            // adapt left padding to the presence of a border:
            echo ".footnote_plugin_index, .footnote_plugin_index_combi {";
            echo "padding-left: 6px !important}\r\n";
        }

        // ref container first column width and max-width:
        $l_bool_ColumnWidthEnabled = MCI_Footnotes_Convert::toBool(MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_BOOL_BACKLINKS_COLUMN_WIDTH_ENABLED));
        $l_bool_ColumnMaxWidthEnabled = MCI_Footnotes_Convert::toBool(MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_BOOL_BACKLINKS_COLUMN_MAX_WIDTH_ENABLED));

        if ( $l_bool_ColumnWidthEnabled || $l_bool_ColumnMaxWidthEnabled ) {
            echo ".footnote-reference-container { table-layout: fixed; }";
            echo ".footnote_plugin_index, .footnote_plugin_index_combi {";

            if ( $l_bool_ColumnWidthEnabled ) {

                $l_int_ColumnWidthScalar = MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_INT_BACKLINKS_COLUMN_WIDTH_SCALAR);
                $l_str_ColumnWidthUnit = MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_STR_BACKLINKS_COLUMN_WIDTH_UNIT);

                if (!empty($l_int_ColumnWidthScalar)) {
                    if ($l_str_ColumnWidthUnit == '%') {
                        if ($l_int_ColumnWidthScalar > 100) {
                            $l_int_ColumnWidthScalar = 100;
                        }
                    }
                } else {
                    $l_int_ColumnWidthScalar = 0;
                }

                echo " width: $l_int_ColumnWidthScalar$l_str_ColumnWidthUnit !important;";
            }

            if ( $l_bool_ColumnMaxWidthEnabled ) {

                $l_int_ColumnMaxWidthScalar = MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_INT_BACKLINKS_COLUMN_MAX_WIDTH_SCALAR);
                $l_str_ColumnMaxWidthUnit = MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_STR_BACKLINKS_COLUMN_MAX_WIDTH_UNIT);

                if (!empty($l_int_ColumnMaxWidthScalar)) {
                    if ($l_str_ColumnMaxWidthUnit == '%') {
                        if ($l_int_ColumnMaxWidthScalar > 100) {
                            $l_int_ColumnMaxWidthScalar = 100;
                        }
                    }
                } else {
                    $l_int_ColumnMaxWidthScalar = 0;
                }

                echo " max-width: $l_int_ColumnMaxWidthScalar$l_str_ColumnMaxWidthUnit !important;";

            }
        echo "}\r\n";
        }

        /**
         * Hard links scroll offset
         *
         * - Bugfix: Scroll offset: make configurable to fix site-dependent issues related to fixed headers.
         *
         * @since 2.1.4
         */
        self::$a_bool_HardLinksEnable = MCI_Footnotes_Convert::toBool(MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_BOOL_FOOTNOTES_HARD_LINKS_ENABLE));
        self::$a_int_ScrollOffset = intval(MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_INT_FOOTNOTES_SCROLL_OFFSET));
        if (self::$a_bool_HardLinksEnable) {
            echo ".footnote_referrer_anchor, .footnote_item_anchor {bottom: ";
            echo self::$a_int_ScrollOffset;
            echo "vh;}\r\n";
        }

        // tooltips:
        self::$a_bool_TooltipsEnabled = MCI_Footnotes_Convert::toBool(MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_BOOL_FOOTNOTES_MOUSE_OVER_BOX_ENABLED));
        self::$a_bool_AlternativeTooltipsEnabled = MCI_Footnotes_Convert::toBool(MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_BOOL_FOOTNOTES_MOUSE_OVER_BOX_ALTERNATIVE));

        if (self::$a_bool_TooltipsEnabled) {

            echo '.footnote_tooltip {';

            // tooltip appearance:

            /**
             * Tooltip font size
             *
             * - Bugfix: Styling: Tooltips: fix font size issue by adding font size to settings with legacy as default.
             *
             * @since 2.1.4
             * @datetime 2020-12-03T0954+0100
             */
            echo ' font-size: ';
            if(MCI_Footnotes_Convert::toBool(MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_BOOL_MOUSE_OVER_BOX_FONT_SIZE_ENABLED))) {
                echo MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_FLO_MOUSE_OVER_BOX_FONT_SIZE_SCALAR);
                echo MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_STR_MOUSE_OVER_BOX_FONT_SIZE_UNIT);
            } else {
                echo 'inherit';
            }
            echo ' !important;';

            // text color:
            $l_str_Color = MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_STR_FOOTNOTES_MOUSE_OVER_BOX_COLOR);
            if (!empty($l_str_Color)) {
                printf(" color: %s !important;", $l_str_Color);
            }

            // background color:
            $l_str_Background = MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_STR_FOOTNOTES_MOUSE_OVER_BOX_BACKGROUND);
            if (!empty($l_str_Background)) {
                printf(" background-color: %s !important;", $l_str_Background);
            }

            // border width:
            $l_int_BorderWidth = MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_INT_FOOTNOTES_MOUSE_OVER_BOX_BORDER_WIDTH);
            if (!empty($l_int_BorderWidth) && intval($l_int_BorderWidth) > 0) {
                printf(" border-width: %dpx !important; border-style: solid !important;", $l_int_BorderWidth);
            }

            // border color:
            $l_str_BorderColor = MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_STR_FOOTNOTES_MOUSE_OVER_BOX_BORDER_COLOR);
            if (!empty($l_str_BorderColor)) {
                printf(" border-color: %s !important;", $l_str_BorderColor);
            }

            // corner radius:
            $l_int_BorderRadius = MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_INT_FOOTNOTES_MOUSE_OVER_BOX_BORDER_RADIUS);
            if (!empty($l_int_BorderRadius) && intval($l_int_BorderRadius) > 0) {
                printf(" border-radius: %dpx !important;", $l_int_BorderRadius);
            }

            // shadow color:
            $l_str_BoxShadowColor = MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_STR_FOOTNOTES_MOUSE_OVER_BOX_SHADOW_COLOR);
            if (!empty($l_str_BoxShadowColor)) {
                printf(" -webkit-box-shadow: 2px 2px 11px %s;", $l_str_BoxShadowColor);
                printf(" -moz-box-shadow: 2px 2px 11px %s;", $l_str_BoxShadowColor);
                printf(" box-shadow: 2px 2px 11px %s;", $l_str_BoxShadowColor);
            }


            /**
             * Tooltip position and timing
             *
             * - Bugfix: Tooltips: make display delays and fade durations configurable to conform to website style.
             *
             * @since 2.1.4
             * @datetime 2020-12-06T1320+0100
             *
             *
             * - Update: Tooltips: Alternative tooltips: connect to position/timing settings (for themes not supporting jQuery tooltips).
             *
             * @since 2.2.5
             * @datetime 2020-12-18T1113+0100
             */
            // alternative tooltips:
            if ( ! self::$a_bool_AlternativeTooltipsEnabled) {

                // tooltip position:
                $l_int_MaxWidth = MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_INT_FOOTNOTES_MOUSE_OVER_BOX_MAX_WIDTH);
                if (!empty($l_int_MaxWidth) && intval($l_int_MaxWidth) > 0) {
                    printf(" max-width: %dpx !important;", $l_int_MaxWidth);
                }
                echo "}\r\n";

            } else {
                echo "}\r\n";

                // position:
                echo ".footnote_tooltip.position {";
                echo " width: " . intval(MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_INT_FOOTNOTES_ALTERNATIVE_MOUSE_OVER_BOX_WIDTH)) . 'px;';

                $l_str_AlternativePosition = MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_STR_FOOTNOTES_ALTERNATIVE_MOUSE_OVER_BOX_POSITION);
                $l_int_OffsetX = intval(MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_INT_FOOTNOTES_ALTERNATIVE_MOUSE_OVER_BOX_OFFSET_X));

                if ($l_str_AlternativePosition == 'top left' || $l_str_AlternativePosition == 'bottom left') {
                    echo ' right: ' . ( !empty($l_int_OffsetX) ? $l_int_OffsetX : 0) . 'px;';
                } else {
                    echo ' left: ' . ( !empty($l_int_OffsetX) ? $l_int_OffsetX : 0) . 'px;';
                }

                $l_int_OffsetY = intval(MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_INT_FOOTNOTES_ALTERNATIVE_MOUSE_OVER_BOX_OFFSET_Y));

                if ($l_str_AlternativePosition == 'top left' || $l_str_AlternativePosition == 'top right') {
                    echo ' bottom: ' . ( !empty($l_int_OffsetY) ? $l_int_OffsetY : 0) . 'px;';
                } else {
                    echo ' top: ' . ( !empty($l_int_OffsetY) ? $l_int_OffsetY : 0) . 'px;';
                }
                echo "}\r\n";

                // timing:
                // jQuery tooltip timing is in templates/public/tooltip.html, filled in after line 690 below.
                echo ' .footnote_tooltip.shown {';
                $l_int_FadeInDelay     = intval(MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_INT_MOUSE_OVER_BOX_FADE_IN_DELAY    ));
                $l_int_FadeInDuration  = intval(MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_INT_MOUSE_OVER_BOX_FADE_IN_DURATION ));
                $l_int_FadeInDelay     = !empty($l_int_FadeInDelay    ) ? $l_int_FadeInDelay     : '0';
                $l_int_FadeInDuration  = !empty($l_int_FadeInDuration ) ? $l_int_FadeInDuration  : '0';
                echo " transition-delay: $l_int_FadeInDelay" . 'ms;';
                echo " transition-duration: $l_int_FadeInDuration" . 'ms;';

                echo '} .footnote_tooltip.hidden {';
                $l_int_FadeOutDelay    = intval(MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_INT_MOUSE_OVER_BOX_FADE_OUT_DELAY   ));
                $l_int_FadeOutDuration = intval(MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_INT_MOUSE_OVER_BOX_FADE_OUT_DURATION));
                $l_int_FadeOutDelay     = !empty($l_int_FadeOutDelay    ) ? $l_int_FadeOutDelay     : '0';
                $l_int_FadeOutDuration  = !empty($l_int_FadeOutDuration ) ? $l_int_FadeOutDuration  : '0';
                echo " transition-delay: $l_int_FadeOutDelay" . 'ms;';
                echo " transition-duration: $l_int_FadeOutDuration" . 'ms;';

                echo "}\r\n";

            }
        }

        /**
         * Custom CSS
         *
         * - Bugfix: Custom CSS: insert new CSS in the public page header element after existing CSS.
         *
         * @since 2.2.3
         * @datetime 2020-12-15T1128+0100
         *
         * Set custom CSS to override settings, not conversely.
         * Legacy Custom CSS is used until it’s set to disappear after dashboard tab migration.
         */
         if (MCI_Footnotes_Convert::toBool(MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_BOOL_CUSTOM_CSS_LEGACY_ENABLE))) {
             echo MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_STR_CUSTOM_CSS);
             echo "\r\n";
        }
        echo MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_STR_CUSTOM_CSS_NEW);

        // insert end tag without switching out of PHP:
        echo "\r\n</style>\r\n";

        /**
         * Alternative tooltip implementation relying on plain JS and CSS transitions.
         *
         * - Bugfix: Tooltips: optional alternative JS implementation with CSS transitions to fix configuration-related outage, thanks to @andreasra feedback.
         *
         * @since 2.1.1
         *
         * @reporter @andreasra
         * @link https://wordpress.org/support/topic/footnotes-appearing-in-header/page/2/#post-13632566
         *
         * The script for alternative tooltips is printed formatted, not minified:
         */
        if ( self::$a_bool_AlternativeTooltipsEnabled ) {
            ?>
            <script content="text/javascript">
                function footnoteTooltipShow(footnoteTooltipId) {
                    document.getElementById(footnoteTooltipId).classList.remove('hidden');
                    document.getElementById(footnoteTooltipId).classList.add('shown');
                }
                function footnoteTooltipHide(footnoteTooltipId) {
                    document.getElementById(footnoteTooltipId).classList.remove('shown');
                    document.getElementById(footnoteTooltipId).classList.add('hidden');
                }
            </script>
            <?php
        };
    }

    /**
     * Displays the 'LOVE FOOTNOTES' slug if enabled.
     *
     * @author Stefan Herndler
     * @since 1.5.0
     *
     *
     * @since 2.2.0  more options  2020-12-11T0506+0100
     */
    public function wp_footer() {
        if (MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_STR_REFERENCE_CONTAINER_POSITION) == "footer") {
            echo $this->ReferenceContainer();
        }
        // get setting for love and share this plugin
        $l_str_LoveMeIndex = MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_STR_FOOTNOTES_LOVE);
        // check if the admin allows to add a link to the footer
        if (empty($l_str_LoveMeIndex) || strtolower($l_str_LoveMeIndex) == "no" || !self::$a_bool_AllowLoveMe) {
            return;
        }
        // set a hyperlink to the word "footnotes" in the Love slug
        $l_str_LinkedName = sprintf('<a href="https://wordpress.org/plugins/footnotes/" target="_blank" style="text-decoration:none;">%s</a>', MCI_Footnotes_Config::C_STR_PLUGIN_PUBLIC_NAME);
        // get random love me text
        if (strtolower($l_str_LoveMeIndex) == "random") {
            $l_str_LoveMeIndex = "text-" . rand(1,7);
        }
        switch ($l_str_LoveMeIndex) {
            // options named wrt backcompat, simplest is default:
            case "text-1": $l_str_LoveMeText = sprintf(__('I %2$s %1$s', MCI_Footnotes_Config::C_STR_PLUGIN_NAME), $l_str_LinkedName, MCI_Footnotes_Config::C_STR_LOVE_SYMBOL); break;
            case "text-2": $l_str_LoveMeText = sprintf(__('This website uses the awesome %s plugin.', MCI_Footnotes_Config::C_STR_PLUGIN_NAME), $l_str_LinkedName); break;
            case "text-4": $l_str_LoveMeText = sprintf('%s %s', $l_str_LinkedName, MCI_Footnotes_Config::C_STR_LOVE_SYMBOL); break;
            case "text-5": $l_str_LoveMeText = sprintf('%s %s', MCI_Footnotes_Config::C_STR_LOVE_SYMBOL, $l_str_LinkedName); break;
            case "text-6": $l_str_LoveMeText = sprintf(__('This website uses %s.', MCI_Footnotes_Config::C_STR_PLUGIN_NAME), $l_str_LinkedName); break;
            case "text-7": $l_str_LoveMeText = sprintf(__('This website uses the %s plugin.', MCI_Footnotes_Config::C_STR_PLUGIN_NAME), $l_str_LinkedName); break;
            case "text-3": default: $l_str_LoveMeText = sprintf('%s', $l_str_LinkedName); break;
        }
        echo sprintf('<div style="text-align:center; color:#acacac;">%s</div>', $l_str_LoveMeText);
    }

    /**
     * Replaces footnotes in the post/page title.
     *
     * @author Stefan Herndler
     * @since 1.5.0
     * @param string $p_str_Content Widget content.
     * @return string Content with replaced footnotes.
     */
    public function the_title($p_str_Content) {
        // appends the reference container if set to "post_end"
        return $this->exec($p_str_Content, false);
    }

    /**
     * Replaces footnotes in the content of the current page/post.
     *
     * @author Stefan Herndler
     * @since 1.5.0
     * @param string $p_str_Content Page/Post content.
     * @return string Content with replaced footnotes.
     */
    public function the_content($p_str_Content) {
        // appends the reference container if set to "post_end"
        return $this->exec($p_str_Content, MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_STR_REFERENCE_CONTAINER_POSITION) == "post_end" ? true : false);
    }

    /**
     * Replaces footnotes in the excerpt of the current page/post.
     *
     * @author Stefan Herndler
     * @since 1.5.0
     * @param string $p_str_Content Page/Post content.
     * @return string Content with replaced footnotes.
     */
    public function the_excerpt($p_str_Content) {
        return $this->exec($p_str_Content, false, !MCI_Footnotes_Convert::toBool(MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_BOOL_FOOTNOTES_IN_EXCERPT)));
    }

    /**
     * Replaces footnotes in the widget title.
     *
     * @author Stefan Herndler
     * @since 1.5.0
     * @param string $p_str_Content Widget content.
     * @return string Content with replaced footnotes.
     */
    public function widget_title($p_str_Content) {
        // appends the reference container if set to "post_end"
        return $this->exec($p_str_Content, false);
    }

    /**
     * Replaces footnotes in the content of the current widget.
     *
     * @author Stefan Herndler
     * @since 1.5.0
     * @param string $p_str_Content Widget content.
     * @return string Content with replaced footnotes.
     */
    public function widget_text($p_str_Content) {
        // appends the reference container if set to "post_end"
        return $this->exec($p_str_Content, MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_STR_REFERENCE_CONTAINER_POSITION) == "post_end" ? true : false);
    }

    /**
     * Replaces footnotes in each Content var of the current Post object.
     *
     * @author Stefan Herndler
     * @since 1.5.4
     * @param array|WP_Post $p_mixed_Posts
     */
    public function the_post(&$p_mixed_Posts) {
        // single WP_Post object received
        if (!is_array($p_mixed_Posts)) {
            $p_mixed_Posts = $this->replacePostObject($p_mixed_Posts);
            return;
        }
        // array of WP_Post objects received
        for($l_int_Index = 0; $l_int_Index < count($p_mixed_Posts); $l_int_Index++) {
            $p_mixed_Posts[$l_int_Index] = $this->replacePostObject($p_mixed_Posts[$l_int_Index]);
        }
    }

    /**
     * Replace all Footnotes in a WP_Post object.
     *
     * @author Stefan Herndler
     * @since 1.5.6
     * @param WP_Post $p_obj_Post
     * @return WP_Post
     */
    private function replacePostObject($p_obj_Post) {
        //MCI_Footnotes_Convert::debug($p_obj_Post);
        $p_obj_Post->post_content = $this->exec($p_obj_Post->post_content);
        $p_obj_Post->post_content_filtered = $this->exec($p_obj_Post->post_content_filtered);
        $p_obj_Post->post_excerpt = $this->exec($p_obj_Post->post_excerpt);
        return $p_obj_Post;
    }

    /**
     * Replaces all footnotes that occur in the given content.
     *
     * @author Stefan Herndler
     * @since 1.5.0
     * @param string $p_str_Content Any string that may contain footnotes to be replaced.
     * @param bool $p_bool_OutputReferences Appends the Reference Container to the output if set to true, default true.
     * @param bool $p_bool_HideFootnotesText Hide footnotes found in the string.
     * @return string
     *
     *
     * @since 2.2.0  Adding: Reference container: support for custom position shortcode, thanks to @hamshe issue report.
     * @since 2.2.5  Bugfix: Reference container: delete position shortcode if unused because position may be widget or footer, thanks to @hamshe bug report.
     */
    public function exec($p_str_Content, $p_bool_OutputReferences = false, $p_bool_HideFootnotesText = false) {

        // replace all footnotes in the content, settings are converted to html characters
        $p_str_Content = $this->search($p_str_Content, true, $p_bool_HideFootnotesText);
        // replace all footnotes in the content, settings are NOT converted to html characters
        $p_str_Content = $this->search($p_str_Content, false, $p_bool_HideFootnotesText);

        /**
         * Reference container customized positioning through shortcode
         *
         * - Adding: Reference container: support for custom position shortcode, thanks to @hamshe issue report.
         *
         * @since 2.2.0
         * @datetime 2020-12-13T2057+0100
         *
         * @reporter @hamshe
         * @link https://wordpress.org/support/topic/reference-container-in-elementor/
         *
         *
         * - Bugfix: Reference container: delete position shortcode if unused because position may be widget or footer, thanks to @hamshe bug report.
         *
         * @since 2.2.5
         * @datetime 2020-12-18T1434+0100
         *
         * @reporter @hamshe
         * @link https://wordpress.org/support/topic/reference-container-in-elementor/#post-13784126
         *
         */
        // append the reference container or insert at shortcode:
        $l_str_ReferenceContainerPositionShortcode = MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_STR_REFERENCE_CONTAINER_POSITION_SHORTCODE);
        if ( empty( $l_str_ReferenceContainerPositionShortcode ) ) {
            $l_str_ReferenceContainerPositionShortcode = '[[references]]';
        }

        if ( $p_bool_OutputReferences ) {

            if ( strpos( $p_str_Content, $l_str_ReferenceContainerPositionShortcode ) !== false ) {

                $p_str_Content = str_replace( $l_str_ReferenceContainerPositionShortcode, $this->ReferenceContainer(), $p_str_Content );

            } else {

                $p_str_Content .= $this->ReferenceContainer();

            }

            // increment the container ID:
            self::$a_int_ReferenceContainerId++;
        }

        // delete position shortcode should any remain:
        $p_str_Content = str_replace( $l_str_ReferenceContainerPositionShortcode, '', $p_str_Content );

        // take a look if the LOVE ME slug should NOT be displayed on this page/post, remove the short code if found
        if (strpos($p_str_Content, MCI_Footnotes_Config::C_STR_NO_LOVE_SLUG) !== false) {
            self::$a_bool_AllowLoveMe = false;
            $p_str_Content = str_replace(MCI_Footnotes_Config::C_STR_NO_LOVE_SLUG, "", $p_str_Content);
        }
        // return the content with replaced footnotes and optional reference container appended:
        return $p_str_Content;
    }

    /**
     * Replaces all footnotes in the given content and appends them to the static property.
     *
     * @author Stefan Herndler
     * @since 1.5.0
     * @param string $p_str_Content Content to be searched for footnotes.
     * @param bool $p_bool_ConvertHtmlChars html encode settings, default true.
     * @param bool $p_bool_HideFootnotesText Hide footnotes found in the string.
     * @return string
     *
     * @since 2.0.0  various.
     * @since 2.4.0  Adding: Footnote delimiters: syntax validation for balanced footnote start and end tag short codes.
     * @since 2.5.0  Bugfix: Footnote delimiters: Syntax validation: exclude certain cases involving scripts, thanks to @andreasra bug report.
     * @since 2.5.0  Bugfix: Footnote delimiters: Syntax validation: complete message with hint about setting, thanks to @andreasra bug report.
     * @since 2.5.0  Bugfix: Footnote delimiters: Syntax validation: limit length of quoted string to 300 characters, thanks to @andreasra bug report.
     */
    public function search($p_str_Content, $p_bool_ConvertHtmlChars, $p_bool_HideFootnotesText) {

        // post ID to make everything unique wrt infinite scroll and archive view
        self::$a_int_PostId = get_the_id();

        // contains the index for the next footnote on this page
        $l_int_FootnoteIndex = count(self::$a_arr_Footnotes) + 1;

        // contains the starting position for the lookup of a footnote
        $l_int_PosStart = 0;

        // get start and end tag for the footnotes short code
        $l_str_StartingTag = MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_STR_FOOTNOTES_SHORT_CODE_START);
        $l_str_EndingTag = MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_STR_FOOTNOTES_SHORT_CODE_END);
        if ($l_str_StartingTag == "userdefined" || $l_str_EndingTag == "userdefined") {
            $l_str_StartingTag = MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_STR_FOOTNOTES_SHORT_CODE_START_USER_DEFINED);
            $l_str_EndingTag = MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_STR_FOOTNOTES_SHORT_CODE_END_USER_DEFINED);
        }
        // decode html special chars
        if ($p_bool_ConvertHtmlChars) {
            $l_str_StartingTag = htmlspecialchars($l_str_StartingTag);
            $l_str_EndingTag = htmlspecialchars($l_str_EndingTag);
        }

        // if footnotes short code is empty, return the content without changes
        if (empty($l_str_StartingTag) || empty($l_str_EndingTag)) {
            return $p_str_Content;
        }

        /**
         * Footnote delimiter syntax validation
         *
         * - Adding: Footnote delimiters: syntax validation for balanced footnote start and end tag short codes.
         *
         * @since 2.4.0
         *
         *
         * - Bugfix: Footnote delimiters: Syntax validation: exclude certain cases involving scripts, thanks to @andreasra bug report.
         * - Bugfix: Footnote delimiters: Syntax validation: complete message with hint about setting, thanks to @andreasra bug report.
         * - Bugfix: Footnote delimiters: Syntax validation: limit length of quoted string to 300 characters, thanks to @andreasra bug report.
         *
         * @since 2.5.0
         * @datetime 2021-01-07T0824+0100
         *
         * @reporter @andreasra
         * @link https://wordpress.org/support/topic/warning-unbalanced-footnote-start-tag-short-code-before/
         *
         *
         * If footnotes short codes are unbalanced, and syntax validation is not disabled,
         * prepend a warning to the content; displays de facto beneath the post title.
         */
        if (MCI_Footnotes_Convert::toBool(MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_BOOL_FOOTNOTE_SHORTCODE_SYNTAX_VALIDATION_ENABLE))) {

            // make shortcodes conform to regex syntax:
            $l_str_StartTagRegex = preg_replace( '#([\(\)\{\}\[\]\*\.\?\!])#', '\\\\$1', $l_str_StartingTag );
            $l_str_EndTagRegex = preg_replace( '#([\(\)\{\}\[\]\*\.\?\!])#', '\\\\$1', $l_str_EndingTag );

            // apply different regex depending on whether start shortcode is double/triple opening parenthesis:
            if ( $l_str_StartingTag == '((' || $l_str_StartingTag == '(((' ) {

                // this prevents from catching a script containing e.g. a double opening parenthesis:
                $l_str_ValidationRegex = '#' . $l_str_StartTagRegex . '(((?!' . $l_str_EndTagRegex . ')[^\{\}])*?)(' . $l_str_StartTagRegex . '|$)#s';

            } else {

                // catch all only if the start shortcode is not double/triple opening parenthesis, i.e. is unlikely to occur in scripts:
                $l_str_ValidationRegex = '#' . $l_str_StartTagRegex . '(((?!' . $l_str_EndTagRegex . ').)*?)(' . $l_str_StartTagRegex . '|$)#s';
            }

            // check syntax and get error locations:
            preg_match( $l_str_ValidationRegex, $p_str_Content, $p_arr_ErrorLocation );
            if ( empty( $p_arr_ErrorLocation ) ) {
                self::$a_bool_SyntaxErrorFlag = false;
            }

            // prevent generating and inserting the warning multiple times:
            if ( self::$a_bool_SyntaxErrorFlag ) {

                // get plain text string for error location:
                $l_str_ErrorSpotString = strip_tags( $p_arr_ErrorLocation[1] );

                // limit string length to 300 characters:
                if ( strlen( $l_str_ErrorSpotString ) > 300 ) {
                    $l_str_ErrorSpotString = substr( $l_str_ErrorSpotString, 0, 299 ) . '…';
                }

                // compose warning box:
                $l_str_SyntaxErrorWarning  = '<div class="footnotes_validation_error"><p>';
                $l_str_SyntaxErrorWarning .= __("WARNING: unbalanced footnote start tag short code found.", MCI_Footnotes_Config::C_STR_PLUGIN_NAME);
                $l_str_SyntaxErrorWarning .= '</p><p>';

                // syntax validation setting in the dashboard under the General settings tab:
                $l_str_SyntaxErrorWarning .= sprintf( __("If this warning is irrelevant, please disable the syntax validation feature in the dashboard under %s &gt; %s &gt; %s.", MCI_Footnotes_Config::C_STR_PLUGIN_NAME), __("General settings", MCI_Footnotes_Config::C_STR_PLUGIN_NAME), __("Footnote start and end short codes", MCI_Footnotes_Config::C_STR_PLUGIN_NAME), __("Check for balanced shortcodes", MCI_Footnotes_Config::C_STR_PLUGIN_NAME) );

                $l_str_SyntaxErrorWarning .= '</p><p>';
                $l_str_SyntaxErrorWarning .= __("Unbalanced start tag short code found before:", MCI_Footnotes_Config::C_STR_PLUGIN_NAME);
                $l_str_SyntaxErrorWarning .= '</p><p>“';
                $l_str_SyntaxErrorWarning .= $l_str_ErrorSpotString;
                $l_str_SyntaxErrorWarning .= '”</p></div>';

                // prepend the warning box to the content:
                $p_str_Content = $l_str_SyntaxErrorWarning . $p_str_Content;

                // checked, set flag to false to prevent duplicate warning:
                self::$a_bool_SyntaxErrorFlag = false;

                return $p_str_Content;
            }
        }


        // load referrer templates if footnotes text not hidden:
        if (!$p_bool_HideFootnotesText) {

            // load footnote referrer template file:
            if (self::$a_bool_AlternativeTooltipsEnabled) {
                $l_obj_Template = new MCI_Footnotes_Template(MCI_Footnotes_Template::C_STR_PUBLIC, "footnote-alternative");
            } else {
                $l_obj_Template = new MCI_Footnotes_Template(MCI_Footnotes_Template::C_STR_PUBLIC, "footnote");
            }

            /**
             * Call Boolean again for robustness when priority levels don’t match any longer.
             *
             * - Bugfix: Tooltips: fix display in Popup Maker popups by correcting a coding error.
             *
             * @since 2.5.4
             * @see self::add_filter('pum_popup_content', array($this, "the_content"), $l_int_TheContentPriority)
             */
            self::$a_bool_TooltipsEnabled = MCI_Footnotes_Convert::toBool(MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_BOOL_FOOTNOTES_MOUSE_OVER_BOX_ENABLED));
            self::$a_bool_AlternativeTooltipsEnabled = MCI_Footnotes_Convert::toBool(MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_BOOL_FOOTNOTES_MOUSE_OVER_BOX_ALTERNATIVE));

            // load tooltip inline script if jQuery tooltips are enabled:
            if (self::$a_bool_TooltipsEnabled && ! self::$a_bool_AlternativeTooltipsEnabled) {
                $l_obj_TemplateTooltip = new MCI_Footnotes_Template(MCI_Footnotes_Template::C_STR_PUBLIC, "tooltip");
            }

        } else {
            $l_obj_Template = null;
            $l_obj_TemplateTooltip = null;
        }

        // search footnotes short codes in the content
        do {
            // get first occurrence of the footnote start tag short code:
            $i_int_LenContent = strlen($p_str_Content);
            if ($l_int_PosStart > $i_int_LenContent) $l_int_PosStart = $i_int_LenContent;
            $l_int_PosStart = strpos($p_str_Content, $l_str_StartingTag, $l_int_PosStart);
            // no short code found, stop here
            if ($l_int_PosStart === false) {
                break;
            }
            // get first occurrence of the footnote end tag short code:
            $l_int_PosEnd = strpos($p_str_Content, $l_str_EndingTag, $l_int_PosStart);
            // no short code found, stop here
            if ($l_int_PosEnd === false) {
                break;
            }
            // calculate the length of the footnote
            $l_int_Length = $l_int_PosEnd - $l_int_PosStart;

            // get footnote text
            $l_str_FootnoteText = substr($p_str_Content, $l_int_PosStart + strlen($l_str_StartingTag), $l_int_Length - strlen($l_str_StartingTag));

            // get tooltip text if present:
            self::$a_str_TooltipShortcode = MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_STR_FOOTNOTES_TOOLTIP_EXCERPT_DELIMITER);
            self::$a_int_TooltipShortcodeLength = strlen( self::$a_str_TooltipShortcode );
            $l_int_TooltipTextLength = strpos( $l_str_FootnoteText, self::$a_str_TooltipShortcode );
            $l_bool_HasTooltipText = $l_int_TooltipTextLength === false ? false : true;
            if ( $l_bool_HasTooltipText ) {
                $l_str_TooltipText = substr( $l_str_FootnoteText, 0, $l_int_TooltipTextLength );
            } else {
                $l_str_TooltipText = '';
            }

            /**
             * URL line wrapping for Unicode non conformant browsers
             *
             * @since 2.1.1 (CSS)
             * @since 2.1.4 (PHP)
             *
             * Despite Unicode recommends to line-wrap URLs at slashes, and Firefox follows
             * the Unicode standard, Chrome does not, making long URLs hang out of tooltips
             * or extend reference containers, so that the end is hidden outside the window
             * and may eventually be viewed after we scroll horizontally or zoom out. It is
             * up to the web page to make URLs breaking anywhere by wrapping them in a span
             * that is assigned appropriate CSS properties and values.
             * @see css/public.css
             *
             * - Bugfix: Tooltips: fix line breaking for hyperlinked URLs in Unicode-non-compliant user agents, thanks to @andreasra bug report.
             *
             * @since 2.1.1
             *
             * @reporter @andreasra
             * @link https://wordpress.org/support/topic/footnotes-appearing-in-header/page/3/#post-13657398
             *
             *
             * - Bugfix: Reference container: fix width in mobile view by URL wrapping for Unicode-non-conformant browsers, thanks to @karolszakiel bug report.
             *
             * @since 2.1.3
             * @date 2020-11-23
             *
             * @reporter @karolszakiel
             * @link https://wordpress.org/support/topic/footnotes-on-mobile-phones/
             *
             *
             * - Bugfix: Reference container, tooltips: fix line wrapping of URLs (hyperlinked or not) based on pattern, not link element.
             *
             * @since 2.1.4
             * @datetime 2020-11-25T0837+0100
             * @link https://wordpress.org/support/topic/footnotes-on-mobile-phones/#post-13710682
             *
             *
             * - Bugfix: Reference container, tooltips: URL wrap: exclude image source too, thanks to @bjrnet21 bug report.
             *
             * @since 2.1.5
             *
             * @reporter @bjrnet21
             * @link https://wordpress.org/support/topic/2-1-4-breaks-on-my-site-images-dont-show/
             *
             *
             * - Bugfix: Reference container, tooltips: URL wrap: fix regex, thanks to @a223123131 bug report.
             *
             * @since 2.1.6
             * @datetime 2020-12-09T1921+0100
             *
             * @reporter @a223123131
             * @link https://wordpress.org/support/topic/broken-layout-starting-version-2-1-4/
             *
             * Even ARIA labels may take a URL as value, so use \w=[\'"] as a catch-all    2020-12-10T1005+0100
             *
             * - Bugfix: Dashboard: URL wrap: add option to properly enable/disable URL wrap.
             *
             * @since 2.1.6
             * @datetime 2020-12-09T1606+0100
             *
             *
             * - Bugfix: Reference container, tooltips: URL wrap: make the quotation mark optional wrt query parameters, thanks to @spiralofhope2 bug report.
             *
             * @since 2.2.6
             * @datetime 2020-12-23T0409+0100
             *
             * @reporter @spiralofhope2
             * @link https://wordpress.org/support/topic/two-links-now-breaks-footnotes-with-blogtext/
             *
             *
             * - Bugfix: Reference container, tooltips: URL wrap: remove a bug introduced in the regex, thanks to @rjl20 @spaceling @lukashuggenberg @klusik @friedrichnorth @bernardzit bug reports.
             *
             * @since 2.2.7
             * @datetime 2020-12-23T1046+0100
             *
             * @reporter @rjl20
             * @link https://wordpress.org/support/topic/two-links-now-breaks-footnotes-with-blogtext/#post-13825479
             *
             * @reporter @spaceling
             * @link https://wordpress.org/support/topic/two-links-now-breaks-footnotes-with-blogtext/#post-13825532
             *
             * @reporter @lukashuggenberg
             * @link https://wordpress.org/support/topic/2-2-6-breaks-all-footnotes/
             *
             * @reporter @klusik
             * @link https://wordpress.org/support/topic/2-2-6-breaks-all-footnotes/#post-13825885
             *
             * @reporter @friedrichnorth
             * @link https://wordpress.org/support/topic/footnotes-dont-show-after-update-to-2-2-6/
             *
             * @reporter @bernardzit
             * @link https://wordpress.org/support/topic/footnotes-dont-show-after-update-to-2-2-6/#post-13826029
             *
             *
             * @since 2.2.8  Bugfix: Reference container, tooltips: URL wrap: correctly make the quotation mark optional wrt query parameters, thanks to @spiralofhope2 bug report.
             * @datetime 2020-12-23T1107+0100
             *
             * Correct is duplicating the negative lookbehind w/o quotes: '(?<!\w=)'
             *
             * @since 2.2.9  Bugfix: Reference container, tooltips: URL wrap: account for RFC 2396 allowed characters in parameter names.
             * @datetime 2020-12-24T1956+0100
             * @link https://stackoverflow.com/questions/814700/http-url-allowed-characters-in-parameter-names
             *
             * @since 2.2.9  Bugfix: Reference container, tooltips: URL wrap: exclude URLs also where the equals sign is preceded by an entity or character reference.
             * @datetime 2020-12-25T1251+0100
             *
             * @since 2.2.10 Bugfix: Reference container, tooltips: URL wrap: support also file transfer protocol URLs.
             * @datetime 2020-12-25T2220+0100
             *
             *
             * - Bugfix: Reference container, tooltips: URL wrap: exclude URL pattern as folder name in Wayback Machine URL, thanks to @rumperuu bug report.
             *
             * @since 2.5.3
             * @date 2021-01-24
             *
             * @reporter @rumperuu
             * @link https://wordpress.org/support/topic/line-wrap-href-regex-bug/
             *
             * By adding a 3rd negative lookbehind: '(?<!/)'.
             *
             *
             * - Bugfix: Reference container, tooltips: URL wrap: account for leading space in value, thanks to @karolszakiel example provision.
             *
             * @since 2.5.4
             * @datetime
             *
             * @reporter @karolszakiel
             * @link https://wordpress.org/support/topic/footnotes-on-mobile-phones/
             *
             * The value of an href argument may have leading (and trailing) space.
             * @link https://webmasters.stackexchange.com/questions/93540/are-spaces-in-href-valid
             * Needs to replicate the relevant negative lookbehind at least with one and with two spaces.
             * Note: The WordPress blog engine edits these values, cropping these leading/trailing spaces.
             *       But given they can occur on WP-powered websites, some page builders may probably not.
             */
            if ( MCI_Footnotes_Convert::toBool( MCI_Footnotes_Settings::instance()->get( MCI_Footnotes_Settings::C_BOOL_FOOTNOTE_URL_WRAP_ENABLED ) ) ) {

                $l_str_FootnoteText = preg_replace(
                    '#(?<![-\w\.!~\*\'\(\);]=[\'"])(?<![-\w\.!~\*\'\(\);]=[\'"] )(?<![-\w\.!~\*\'\(\);]=[\'"]  )(?<![-\w\.!~\*\'\(\);]=)(?<!/)((ht|f)tps?://[^\\s<]+)#',
                    '<span class="footnote_url_wrap">$1</span>',
                    $l_str_FootnoteText
                );
            }

            // Text to be displayed instead of the footnote
            $l_str_FootnoteReplaceText = "";

            // whether hard links are enabled:
            if (self::$a_bool_HardLinksEnable) {

                // get the configurable parts:
                self::$a_str_ReferrerLinkSlug = MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_STR_REFERRER_FRAGMENT_ID_SLUG);
                self::$a_str_FootnoteLinkSlug = MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_STR_FOOTNOTE_FRAGMENT_ID_SLUG);
                self::$a_str_LinkIdsSeparator = MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_STR_HARD_LINK_IDS_SEPARATOR);

                // streamline ID concatenation:
                self::$a_str_PostContainerIdCompound  = self::$a_str_LinkIdsSeparator;
                self::$a_str_PostContainerIdCompound .= self::$a_int_PostId;
                self::$a_str_PostContainerIdCompound .= self::$a_str_LinkIdsSeparator;
                self::$a_str_PostContainerIdCompound .= self::$a_int_ReferenceContainerId;
                self::$a_str_PostContainerIdCompound .= self::$a_str_LinkIdsSeparator;

            }

            // display the footnote referrers and the tooltips:
            if (!$p_bool_HideFootnotesText) {
                $l_int_Index = MCI_Footnotes_Convert::Index($l_int_FootnoteIndex, MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_STR_FOOTNOTES_COUNTER_STYLE));

                // display only a truncated footnote text if option enabled:
                $l_bool_EnableExcerpt = MCI_Footnotes_Convert::toBool(MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_BOOL_FOOTNOTES_MOUSE_OVER_BOX_EXCERPT_ENABLED));
                $l_int_MaxLength = intval(MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_INT_FOOTNOTES_MOUSE_OVER_BOX_EXCERPT_LENGTH));

                // define excerpt text as footnote text by default:
                $l_str_ExcerptText = $l_str_FootnoteText;

                /**
                 * Tooltip truncation
                 *
                 * - Adding: Tooltips: Read-on button: Label: configurable instead of localizable, thanks to @rovanov example provision.
                 *
                 * @since 2.1.0
                 * @datetime 2020-11-08T2146+0100
                 *
                 * @reporter @rovanov
                 * @link https://wordpress.org/support/topic/offset-x-axis-and-offset-y-axis-does-not-working/
                 *
                 * If the tooltip truncation option is enabled, it’s done based on character count,
                 * and a trailing incomplete word is cropped.
                 * This is equivalent to the WordPress default excerpt generation, i.e. without a
                 * custom excerpt and without a delimiter. But WordPress does word count, usually 55.
                 */
                if (self::$a_bool_TooltipsEnabled && $l_bool_EnableExcerpt) {
                    $l_str_DummyText = strip_tags($l_str_FootnoteText);
                    if (is_int($l_int_MaxLength) && strlen($l_str_DummyText) > $l_int_MaxLength) {
                        $l_str_ExcerptText  = substr($l_str_DummyText, 0, $l_int_MaxLength);
                        $l_str_ExcerptText  = substr($l_str_ExcerptText, 0, strrpos($l_str_ExcerptText, ' '));
                        $l_str_ExcerptText .= '&nbsp;&#x2026; <';
                        $l_str_ExcerptText .= self::$a_bool_HardLinksEnable ? 'a' : 'span';
                        $l_str_ExcerptText .= ' class="footnote_tooltip_continue" ';
                        $l_str_ExcerptText .= 'onclick="footnote_moveToAnchor_' . self::$a_int_PostId;
                        $l_str_ExcerptText .= '_' . self::$a_int_ReferenceContainerId;
                        $l_str_ExcerptText .= '(\'footnote_plugin_reference_' . self::$a_int_PostId;
                        $l_str_ExcerptText .= '_' . self::$a_int_ReferenceContainerId;
                        $l_str_ExcerptText .= "_$l_int_Index');\"";

                        // if enabled, add the hard link fragment ID:
                        if (self::$a_bool_HardLinksEnable) {

                            $l_str_ExcerptText .= ' href="#';
                            $l_str_ExcerptText .= self::$a_str_FootnoteLinkSlug;
                            $l_str_ExcerptText .= self::$a_str_PostContainerIdCompound;
                            $l_str_ExcerptText .= $l_int_Index;
                            $l_str_ExcerptText .= '"';
                        }

                        $l_str_ExcerptText .= '>';

                        /**
                         * Configurable read-on button label
                         *
                         * - Adding: Tooltips: Read-on button: Label: configurable instead of localizable, thanks to @rovanov example provision.
                         *
                         * @since 2.1.0
                         * @datetime 2020-11-08T2146+0100
                         *
                         * @reporter @rovanov
                         * @link https://wordpress.org/support/topic/offset-x-axis-and-offset-y-axis-does-not-working/
                         */
                        $l_str_ExcerptText .= MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_STR_FOOTNOTES_TOOLTIP_READON_LABEL);

                        $l_str_ExcerptText .= self::$a_bool_HardLinksEnable ? '</a>' : '</span>';
                    }
                }

                /**
                 * Referrers element superscript or baseline
                 *
                 * Referrers: new setting for vertical align: superscript (default) or baseline (optional), thanks to @cwbayer bug report
                 * @since 2.1.1
                 *
                 * @reporter @cwbayer
                 * @link https://wordpress.org/support/topic/footnote-number-in-text-superscript-disrupts-leading/
                 *
                 * define the HTML element to use for the referrers:
                 */
                if (MCI_Footnotes_Convert::toBool(MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_BOOL_FOOTNOTES_REFERRER_SUPERSCRIPT_TAGS))) {

                    $l_str_SupSpan = 'sup';

                } else {

                    $l_str_SupSpan = 'span';
                }

                // whether hard links are enabled:
                if (self::$a_bool_HardLinksEnable) {

                    self::$a_str_LinkSpan = 'a';
                    self::$a_str_LinkCloseTag = '</a>';
                    // self::$a_str_LinkOpenTag will be defined as needed

                    // compose hyperlink address (leading space is in template):
                    $l_str_FootnoteLinkArgument  = 'href="#';
                    $l_str_FootnoteLinkArgument .= self::$a_str_FootnoteLinkSlug;
                    $l_str_FootnoteLinkArgument .= self::$a_str_PostContainerIdCompound;
                    $l_str_FootnoteLinkArgument .= $l_int_Index;
                    $l_str_FootnoteLinkArgument .= '" class="footnote_hard_link"';

                    /**
                     * Compose fragment ID anchor with offset, for use in reference container.
                     * Empty span, child of empty span, to avoid tall dotted rectangles in browser.
                     */
                    $l_str_ReferrerAnchorElement  = '<span class="footnote_referrer_base"><span id="';
                    $l_str_ReferrerAnchorElement .= self::$a_str_ReferrerLinkSlug;
                    $l_str_ReferrerAnchorElement .= self::$a_str_PostContainerIdCompound;
                    $l_str_ReferrerAnchorElement .= $l_int_Index;
                    $l_str_ReferrerAnchorElement .= '" class="footnote_referrer_anchor"></span></span>';

                } else {

                    /**
                     * Initialize hard link variables when hard links are disabled.
                     *
                     * - Bugfix: Process: initialize hard link address variables to empty string to fix 'undefined variable' bug, thanks to @a223123131 bug report.
                     *
                     * @since 2.4.0
                     * @datetime 2021-01-04T1622+0100
                     *
                     * @reporter @a223123131
                     * @link https://wordpress.org/support/topic/wp_debug-php-notice/
                     *
                     * If no hyperlink nor offset anchor is needed, initialize as empty.
                     */
                    $l_str_FootnoteLinkArgument = '';
                    $l_str_ReferrerAnchorElement = '';

                    // The link element is set independently as it may be needed for styling:
                    if ( MCI_Footnotes_Convert::toBool(MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_BOOL_LINK_ELEMENT_ENABLED)) ) {

                        self::$a_str_LinkSpan = 'a';
                        self::$a_str_LinkOpenTag = '<a>';
                        self::$a_str_LinkCloseTag = '</a>';

                    }
                }

                // determine tooltip content:
                if ( self::$a_bool_TooltipsEnabled ) {
                    $l_str_TooltipContent = $l_bool_HasTooltipText ? $l_str_TooltipText : $l_str_ExcerptText;
                } else {
                    $l_str_TooltipContent = '';
                }

                // fill in 'templates/public/footnote.html':
                $l_obj_Template->replace(
                    array(
                        "link-span"      => self::$a_str_LinkSpan,
                        "post_id"        => self::$a_int_PostId,
                        "container_id"   => self::$a_int_ReferenceContainerId,
                        "note_id"        => $l_int_Index,
                        "hard-link"      => $l_str_FootnoteLinkArgument,
                        "sup-span"       => $l_str_SupSpan,
                        "before"         => MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_STR_FOOTNOTES_STYLING_BEFORE),
                        "index"          => $l_int_Index,
                        "after"          => MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_STR_FOOTNOTES_STYLING_AFTER),
                        "anchor-element" => $l_str_ReferrerAnchorElement,
                        "text"           => $l_str_TooltipContent,
                    )
                );
                $l_str_FootnoteReplaceText = $l_obj_Template->getContent();

                // reset the template
                $l_obj_Template->reload();

                // if standard tooltips are enabled but alternative are not:
                if (self::$a_bool_TooltipsEnabled && ! self::$a_bool_AlternativeTooltipsEnabled) {

                    $l_int_OffsetY         = intval(MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_INT_FOOTNOTES_MOUSE_OVER_BOX_OFFSET_Y));
                    $l_int_OffsetX         = intval(MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_INT_FOOTNOTES_MOUSE_OVER_BOX_OFFSET_X));
                    $l_int_FadeInDelay     = intval(MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_INT_MOUSE_OVER_BOX_FADE_IN_DELAY    ));
                    $l_int_FadeInDuration  = intval(MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_INT_MOUSE_OVER_BOX_FADE_IN_DURATION ));
                    $l_int_FadeOutDelay    = intval(MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_INT_MOUSE_OVER_BOX_FADE_OUT_DELAY   ));
                    $l_int_FadeOutDuration = intval(MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_INT_MOUSE_OVER_BOX_FADE_OUT_DURATION));

                    // fill in 'templates/public/tooltip.html':
                    $l_obj_TemplateTooltip->replace(
                        array(
                            "post_id"           => self::$a_int_PostId,
                            "container_id"      => self::$a_int_ReferenceContainerId,
                            "note_id"           => $l_int_Index,
                            "position"          => MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_STR_FOOTNOTES_MOUSE_OVER_BOX_POSITION),
                            "offset-y"          => !empty($l_int_OffsetY) ? $l_int_OffsetY : 0,
                            "offset-x"          => !empty($l_int_OffsetX) ? $l_int_OffsetX : 0,
                            "fade-in-delay"     => !empty($l_int_FadeInDelay    ) ? $l_int_FadeInDelay     : 0,
                            "fade-in-duration"  => !empty($l_int_FadeInDuration ) ? $l_int_FadeInDuration  : 0,
                            "fade-out-delay"    => !empty($l_int_FadeOutDelay   ) ? $l_int_FadeOutDelay    : 0,
                            "fade-out-duration" => !empty($l_int_FadeOutDuration) ? $l_int_FadeOutDuration : 0,
                        )
                    );
                    $l_str_FootnoteReplaceText .= $l_obj_TemplateTooltip->getContent();
                    $l_obj_TemplateTooltip->reload();
                }
            }
            // replace the footnote with the template
            $p_str_Content = substr_replace($p_str_Content, $l_str_FootnoteReplaceText, $l_int_PosStart, $l_int_Length + strlen($l_str_EndingTag));

            // add footnote only if not empty
            if (!empty($l_str_FootnoteText)) {
                // set footnote to the output box at the end
                self::$a_arr_Footnotes[] = $l_str_FootnoteText;
                // increase footnote index
                $l_int_FootnoteIndex++;
            }
            // add offset to the new starting position
            $l_int_PosStart += $l_int_Length + strlen($l_str_EndingTag);
            $l_int_PosStart = $l_int_Length + strlen($l_str_FootnoteReplaceText);
        } while (true);

        // return content
        return $p_str_Content;
    }

    /**
     * Generates the reference container.
     *
     * @author Stefan Herndler
     * @since 1.5.0
     * @return string
     *
     * @since 2.0.0  Update: remove backlink symbol along with column 2 of the reference container
     * @since 2.0.3  Bugfix: prepend an arrow on user request
     * @since 2.0.6  Bugfix: Reference container: fix line breaking behavior in footnote number clusters.
     * @since 2.0.4  Bugfix: restore the arrow select and backlink symbol input settings
     * @since 2.1.1  Bugfix: Referrers, reference container: Combining identical footnotes: fix dead links and ensure referrer-backlink bijectivity, thanks to @happyches bug report.
     * @since 2.1.1  Bugfix: Reference container: Backlink symbol: make optional, not suggest configuring it to invisible, thanks to @spaceling feedback.
     */
    public function ReferenceContainer() {

        // no footnotes have been replaced on this page:
        if (empty(self::$a_arr_Footnotes)) {
            return "";
        }


        /**
         * Footnote index backlink symbol
         *
         * - Bugfix: Reference container: Backlink symbol: make optional, not suggest configuring it to invisible, thanks to @spaceling feedback.
         *
         * @since 2.1.1
         *
         * @reporter @spaceling
         * @link https://wordpress.org/support/topic/change-the-position-5/page/2/#post-13671138
         *
         * If the backlink symbol is enabled:
         */
        if (MCI_Footnotes_Convert::toBool(MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_BOOL_REFERENCE_CONTAINER_BACKLINK_SYMBOL_ENABLE))) {

            // get html arrow
            $l_str_Arrow = MCI_Footnotes_Convert::getArrow(MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_STR_HYPERLINK_ARROW));
            // set html arrow to the first one if invalid index defined
            if (is_array($l_str_Arrow)) {
                $l_str_Arrow = MCI_Footnotes_Convert::getArrow(0);
            }
            // get user defined arrow
            $l_str_ArrowUserDefined = MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_STR_HYPERLINK_ARROW_USER_DEFINED);
            if (!empty($l_str_ArrowUserDefined)) {
                $l_str_Arrow = $l_str_ArrowUserDefined;
            }

            // wrap the arrow in a @media print { display:hidden } span:
            $l_str_FootnoteArrow  = '<span class="footnote_index_arrow">';
            $l_str_FootnoteArrow .= $l_str_Arrow . '</span>';

        } else {

            // If the backlink symbol isn’t enabled, set it to empty:
            $l_str_Arrow = '';
            $l_str_FootnoteArrow = '';

        }


        /**
         * Backlink separator
         *
         * - Bugfix: Reference container: make separating and terminating punctuation optional and configurable, thanks to @docteurfitness issue report and code contribution.
         *
         * @since 2.1.4
         * @datetime 2020-11-28T1048+0100
         *
         * @contributor @docteurfitness
         * @link https://wordpress.org/support/topic/update-2-1-3/#post-13704194
         *
         * @reporter @docteurfitness
         * @link https://wordpress.org/support/topic/update-2-1-3/
         *
         * Initially a comma was appended in this algorithm for enumerations.
         * The comma in enumerations is not generally preferred.
         */
        if (MCI_Footnotes_Convert::toBool(MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_BOOL_BACKLINKS_SEPARATOR_ENABLED))) {

            // check if it is input-configured:
            $l_str_Separator = MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_STR_BACKLINKS_SEPARATOR_CUSTOM);

            if (empty($l_str_Separator)) {

                // if it is not, check which option is on:
                $l_str_SeparatorOption = MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_STR_BACKLINKS_SEPARATOR_OPTION);
                switch ($l_str_SeparatorOption) {
                    case 'comma'    : $l_str_Separator = ',';              break;
                    case 'semicolon': $l_str_Separator = ';';              break;
                    case 'en_dash'  : $l_str_Separator = '&nbsp;&#x2013;'; break;
                }
            }

        } else {

            $l_str_Separator = '';
        }

        /**
         * Backlink terminator
         *
         * Initially a dot was appended in the table row template.
         * @since 2.0.6 a dot after footnote numbers is discarded as not localizable;
         * making it optional was envisaged.
         * @since 2.1.4 the terminator is optional, has options, and is configurable:
         */
        if (MCI_Footnotes_Convert::toBool(MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_BOOL_BACKLINKS_TERMINATOR_ENABLED))) {

            // check if it is input-configured:
            $l_str_Terminator = MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_STR_BACKLINKS_TERMINATOR_CUSTOM);

            if (empty($l_str_Terminator)) {

                // if it is not, check which option is on:
                $l_str_TerminatorOption = MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_STR_BACKLINKS_TERMINATOR_OPTION);
                switch ($l_str_TerminatorOption) {
                    case 'period'     : $l_str_Terminator = '.'; break;
                    case 'parenthesis': $l_str_Terminator = ')'; break;
                    case 'colon'      : $l_str_Terminator = ':'; break;
                }
            }

        } else {

            $l_str_Terminator = '';
        }


        /**
         * Line breaks
         *
         * - Bugfix: Reference container: Backlinks: fix stacked enumerations by adding optional line breaks.
         *
         * @since 2.1.4
         * @datetime 2020-11-28T1049+0100
         *
         * The backlinks of combined footnotes are generally preferred in an enumeration.
         * But when few footnotes are identical, stacking the items in list form is better.
         * Variable number length and proportional character width require explicit line breaks.
         * Otherwise, an ordinary space character offering a line break opportunity is inserted.
         */
        $l_str_LineBreak = MCI_Footnotes_Convert::toBool(MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_BOOL_BACKLINKS_LINE_BREAKS_ENABLED)) ? '<br />' : ' ';

        /**
         * For maintenance and support, table rows in the reference container should be
         * separated by an empty line. So we add these line breaks for source readability.
         * Before the first table row (breaks between rows are ~200 lines below):
         */
        $l_str_Body = "\r\n\r\n";


        /**
         * Reference container table row template load
         *
         * - Bugfix: Reference container: option to restore pre-2.0.0 layout with the backlink symbol in an extra column.
         *
         * @since 2.1.1
         * @datetime 2020-11-16T2024+0100
         */

        // when combining identical footnotes is turned on, another template is needed:
        if (MCI_Footnotes_Convert::toBool(MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_BOOL_COMBINE_IDENTICAL_FOOTNOTES))) {
            // the combining template allows for backlink clusters and supports cell clicking for single notes:
            $l_obj_Template = new MCI_Footnotes_Template(MCI_Footnotes_Template::C_STR_PUBLIC, "reference-container-body-combi");

        } else {

            // when 3-column layout is turned on (only available if combining is turned off):
            if (MCI_Footnotes_Convert::toBool(MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_BOOL_REFERENCE_CONTAINER_3COLUMN_LAYOUT_ENABLE))) {
                $l_obj_Template = new MCI_Footnotes_Template(MCI_Footnotes_Template::C_STR_PUBLIC, "reference-container-body-3column");

            } else {

                // when switch symbol and index is turned on, and combining and 3-columns are off:
                if (MCI_Footnotes_Convert::toBool(MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_BOOL_REFERENCE_CONTAINER_BACKLINK_SYMBOL_SWITCH))) {
                    $l_obj_Template = new MCI_Footnotes_Template(MCI_Footnotes_Template::C_STR_PUBLIC, "reference-container-body-switch");

                } else {

                    // default is the standard template:
                    $l_obj_Template = new MCI_Footnotes_Template(MCI_Footnotes_Template::C_STR_PUBLIC, "reference-container-body");

                }
            }
        }

        /**
         * Switch backlink symbol and footnote number
         *
         * - Bugfix: Reference container: option to append symbol (prepended by default), thanks to @spaceling code contribution.
         *
         * @since 2.1.1
         * @datetime 2020-11-16T2024+0100
         *
         * @contributor @spaceling
         * @link https://wordpress.org/support/topic/change-the-position-5/#post-13615994
         *
         *
         * - Bugfix: Reference container: Backlink symbol: support for appending when combining identicals is on.
         *
         * @since 2.1.4
         * @datetime 2020-11-26T1633+0100
         */
        $l_bool_SymbolSwitch = MCI_Footnotes_Convert::toBool(MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_BOOL_REFERENCE_CONTAINER_BACKLINK_SYMBOL_SWITCH));

        // loop through all footnotes found in the page
        for ($l_int_Index = 0; $l_int_Index < count(self::$a_arr_Footnotes); $l_int_Index++) {

            // get footnote text
            $l_str_FootnoteText = self::$a_arr_Footnotes[$l_int_Index];

            // if footnote is empty, go to the next one;
            // With combine identicals turned on, identicals will be deleted and are skipped:
            if (empty($l_str_FootnoteText)) {
                continue;
            }

            // generate content of footnote index cell
            $l_int_FirstFootnoteIndex = ($l_int_Index + 1);

            // get the footnote index string and
            // keep supporting legacy index placeholder:
            $l_str_FootnoteId  = MCI_Footnotes_Convert::Index(($l_int_Index + 1),  MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_STR_FOOTNOTES_COUNTER_STYLE));

            /**
             * Case of only one backlink per table row
             *
             * If enabled, and for the case the footnote is single, compose hard link:
             */
            // define anyway:
            $l_str_HardLinkAddress = '';

            if (self::$a_bool_HardLinksEnable) {

                /**
                 * Use-Backbutton-Hint tooltip, optional and configurable.
                 *
                 * - Update: Reference container: Hard backlinks (optional): optional configurable tooltip hinting to use the backbutton instead, thanks to @@theroninjedi47 bug report.
                 *
                 * @since 2.5.4
                 *
                 * @reporter @@theroninjedi47
                 * @link https://wordpress.org/support/topic/hyperlinked-footnotes-creating-excessive-back-history/
                 *
                 * When hard links are enabled, clicks on the backlinks are logged in the browsing history.
                 * This tooltip hints to use the backbutton instead, so the history gets streamlined again.
                 * @link https://wordpress.org/support/topic/making-it-amp-compatible/#post-13837359
                 */
                if ( MCI_Footnotes_Convert::toBool( MCI_Footnotes_Settings::instance()->get( MCI_Footnotes_Settings::C_BOOL_FOOTNOTES_BACKLINK_TOOLTIP_ENABLE ) ) ) {
                    $l_str_UseBackbuttonHint  = ' title="';
                    $l_str_UseBackbuttonHint .= MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_STR_FOOTNOTES_BACKLINK_TOOLTIP_TEXT);
                    $l_str_UseBackbuttonHint .= '"';
                } else {
                    $l_str_UseBackbuttonHint = '';
                }

                /**
                 * Compose fragment ID anchor with offset, for use in reference container.
                 * Empty span, child of empty span, to avoid tall dotted rectangles in browser.
                 */
                $l_str_FootnoteAnchorElement  = '<span class="footnote_item_base"><span id="';
                $l_str_FootnoteAnchorElement .= self::$a_str_FootnoteLinkSlug;
                $l_str_FootnoteAnchorElement .= self::$a_str_PostContainerIdCompound;
                $l_str_FootnoteAnchorElement .= $l_str_FootnoteId;
                $l_str_FootnoteAnchorElement .= '" class="footnote_item_anchor"></span></span>';

                // compose optional hard link address:
                $l_str_HardLinkAddress  = ' href="#';
                $l_str_HardLinkAddress .= self::$a_str_ReferrerLinkSlug;
                $l_str_HardLinkAddress .= self::$a_str_PostContainerIdCompound;
                $l_str_HardLinkAddress .= $l_str_FootnoteId . '"';
                $l_str_HardLinkAddress .= $l_str_UseBackbuttonHint;

                // compose optional opening link tag with optional hard link, mandatory for instance:
                self::$a_str_LinkOpenTag  = '<a' . $l_str_HardLinkAddress;
                self::$a_str_LinkOpenTag  = ' class="footnote_hard_back_link">';

            } else {
                // define as empty, too:
                $l_str_FootnoteAnchorElement = '';
            }


            /**
             * Support for combining identicals: compose enumerated backlinks
             *
             * - Bugfix: Referrers, reference container: Combining identical footnotes: fix dead links and ensure referrer-backlink bijectivity, thanks to @happyches bug report.
             *
             * @since 2.1.1
             * @datetime 2020-11-14T2233+0100
             *
             * @reporter @happyches
             * @link https://wordpress.org/support/topic/custom-css-for-jumbled-references/
             *
             * Prepare to have single footnotes, where the click event and
             * optional hard link need to be set to cover the table cell,
             * for better usability and UX.
             */
            // set a flag to check for the combined status of a footnote item:
            $l_bool_FlagCombined = false;

            // set otherwise unused variables as empty to avoid screwing up the placeholder array:
            $l_str_BacklinkEvent     = '';
            $l_str_FootnoteBacklinks = '';
            $l_str_FootnoteReference = '';

            if ( MCI_Footnotes_Convert::toBool(MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_BOOL_COMBINE_IDENTICAL_FOOTNOTES))) {

                // ID, optional hard link address, and class:
                $l_str_FootnoteReference  = '<' . self::$a_str_LinkSpan;
                $l_str_FootnoteReference .= ' id="footnote_plugin_reference_';
                $l_str_FootnoteReference .= self::$a_int_PostId;
                $l_str_FootnoteReference .= '_' . self::$a_int_ReferenceContainerId;
                $l_str_FootnoteReference .= "_$l_str_FootnoteId\"";
                if (self::$a_bool_HardLinksEnable) {
                    $l_str_FootnoteReference .= ' href="#';
                    $l_str_FootnoteReference .= self::$a_str_ReferrerLinkSlug;
                    $l_str_FootnoteReference .= self::$a_str_PostContainerIdCompound;
                    $l_str_FootnoteReference .= $l_str_FootnoteId . '"';
                    $l_str_FootnoteReference .= $l_str_UseBackbuttonHint;
                }
                $l_str_FootnoteReference .= ' class="footnote_backlink"';

                // the click event goes in the table cell if footnote remains single:
                $l_str_BacklinkEvent  = ' onclick="footnote_moveToAnchor_';
                $l_str_BacklinkEvent .= self::$a_int_PostId;
                $l_str_BacklinkEvent .= '_' . self::$a_int_ReferenceContainerId;
                $l_str_BacklinkEvent .= "('footnote_plugin_tooltip_";
                $l_str_BacklinkEvent .= self::$a_int_PostId;
                $l_str_BacklinkEvent .= '_' . self::$a_int_ReferenceContainerId;
                $l_str_BacklinkEvent .= "_$l_str_FootnoteId');\"";


                // the dedicated template enumerating backlinks uses another variable:
                $l_str_FootnoteBacklinks  = $l_str_FootnoteReference;

                // append the click event right to the backlink item for enumerations;
                // else it goes in the table cell:
                $l_str_FootnoteBacklinks .= $l_str_BacklinkEvent . '>';
                $l_str_FootnoteReference .= '>';

                // append the optional offset anchor for hard links:
                if (self::$a_bool_HardLinksEnable) {
                    $l_str_FootnoteReference .= $l_str_FootnoteAnchorElement;
                    $l_str_FootnoteBacklinks .= $l_str_FootnoteAnchorElement;
                }

                // continue both single note and notes cluster, depending on switch option status:
                if ($l_bool_SymbolSwitch) {

                    $l_str_FootnoteReference .= "$l_str_FootnoteId$l_str_FootnoteArrow";
                    $l_str_FootnoteBacklinks .= "$l_str_FootnoteId$l_str_FootnoteArrow";

                } else {

                    $l_str_FootnoteReference .= "$l_str_FootnoteArrow$l_str_FootnoteId";
                    $l_str_FootnoteBacklinks .= "$l_str_FootnoteArrow$l_str_FootnoteId";

                }

                // If that is the only footnote with this text, we’re almost done.

                // check if it isn't the last footnote in the array:
                if ($l_int_FirstFootnoteIndex < count(self::$a_arr_Footnotes)) {

                    // get all footnotes that haven't passed yet:
                    for ($l_int_CheckIndex = $l_int_FirstFootnoteIndex; $l_int_CheckIndex < count(self::$a_arr_Footnotes); $l_int_CheckIndex++) {

                        // check if a further footnote is the same as the actual one:
                        if ($l_str_FootnoteText == self::$a_arr_Footnotes[$l_int_CheckIndex]) {

                            // if so, set the further footnote as empty so it won't be displayed later:
                            self::$a_arr_Footnotes[$l_int_CheckIndex] = "";

                            // set the flag to true for the combined status:
                            $l_bool_FlagCombined = true;

                            // update the footnote ID:
                            $l_str_FootnoteId = MCI_Footnotes_Convert::Index(($l_int_CheckIndex + 1), MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_STR_FOOTNOTES_COUNTER_STYLE));

                            // resume composing the backlinks enumeration:
                            $l_str_FootnoteBacklinks .= "$l_str_Separator</";
                            $l_str_FootnoteBacklinks .= self::$a_str_LinkSpan . '>';
                            $l_str_FootnoteBacklinks .= $l_str_LineBreak;
                            $l_str_FootnoteBacklinks .= '<' . self::$a_str_LinkSpan;
                            $l_str_FootnoteBacklinks .= ' id="footnote_plugin_reference_';
                            $l_str_FootnoteBacklinks .= self::$a_int_PostId;
                            $l_str_FootnoteBacklinks .= '_' . self::$a_int_ReferenceContainerId;
                            $l_str_FootnoteBacklinks .= "_$l_str_FootnoteId\"";

                            // insert the optional hard link address:
                            if (self::$a_bool_HardLinksEnable) {
                                $l_str_FootnoteBacklinks .= ' href="#';
                                $l_str_FootnoteBacklinks .= self::$a_str_ReferrerLinkSlug;
                                $l_str_FootnoteBacklinks .= self::$a_str_PostContainerIdCompound;
                                $l_str_FootnoteBacklinks .= $l_str_FootnoteId . '"';
                                $l_str_FootnoteBacklinks .= $l_str_UseBackbuttonHint;
                            }

                            $l_str_FootnoteBacklinks .= ' class="footnote_backlink"';
                            $l_str_FootnoteBacklinks .= ' onclick="footnote_moveToAnchor_';
                            $l_str_FootnoteBacklinks .= self::$a_int_PostId;
                            $l_str_FootnoteBacklinks .= '_' . self::$a_int_ReferenceContainerId;
                            $l_str_FootnoteBacklinks .= "('footnote_plugin_tooltip_";
                            $l_str_FootnoteBacklinks .= self::$a_int_PostId;
                            $l_str_FootnoteBacklinks .= '_' . self::$a_int_ReferenceContainerId;
                            $l_str_FootnoteBacklinks .= "_$l_str_FootnoteId');\">";

                            // append the offset anchor for optional hard links:
                            if (self::$a_bool_HardLinksEnable) {
                                $l_str_FootnoteBacklinks .= '<span class="footnote_item_base"><span id="';
                                $l_str_FootnoteBacklinks .= self::$a_str_FootnoteLinkSlug;
                                $l_str_FootnoteBacklinks .= self::$a_str_PostContainerIdCompound;
                                $l_str_FootnoteBacklinks .= $l_str_FootnoteId;
                                $l_str_FootnoteBacklinks .= '" class="footnote_item_anchor"></span></span>';
                            }

                            $l_str_FootnoteBacklinks .= $l_bool_SymbolSwitch ? '' : $l_str_FootnoteArrow;
                            $l_str_FootnoteBacklinks .= $l_str_FootnoteId;
                            $l_str_FootnoteBacklinks .= $l_bool_SymbolSwitch ? $l_str_FootnoteArrow : '';

                        }
                    }
                }

                // append terminator and end tag:
                $l_str_FootnoteReference .= $l_str_Terminator . '</' . self::$a_str_LinkSpan . '>';
                $l_str_FootnoteBacklinks .= $l_str_Terminator . '</' . self::$a_str_LinkSpan . '>';

            }

            // line wrapping of URLs already fixed, see above

            // get reference container item text if tooltip text goes separate:
            $l_int_TooltipTextLength = strpos( $l_str_FootnoteText, self::$a_str_TooltipShortcode );
            $l_bool_HasTooltipText = $l_int_TooltipTextLength === false ? false : true;
            if ( $l_bool_HasTooltipText ) {
                $l_str_NotTooltipText = substr( $l_str_FootnoteText, ( $l_int_TooltipTextLength + self::$a_int_TooltipShortcodeLength ) );
                self::$a_bool_MirrorTooltipText = MCI_Footnotes_Convert::toBool( MCI_Footnotes_Settings::instance()->get( MCI_Footnotes_Settings::C_BOOL_FOOTNOTES_TOOLTIP_EXCERPT_MIRROR_ENABLE ) );
                if ( self::$a_bool_MirrorTooltipText ) {
                    $l_str_TooltipText = substr( $l_str_FootnoteText, 0, $l_int_TooltipTextLength );
                    $l_str_ReferenceTextIntroducer = MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_STR_FOOTNOTES_TOOLTIP_EXCERPT_MIRROR_SEPARATOR);
                    $l_str_ReferenceText = $l_str_TooltipText . $l_str_ReferenceTextIntroducer . $l_str_NotTooltipText;
                } else {
                    $l_str_ReferenceText = $l_str_NotTooltipText;
                }
            } else {
                $l_str_ReferenceText = $l_str_FootnoteText;
            }

            // replace all placeholders in table row template:
            $l_obj_Template->replace(
                array(

                    // placeholder used in all templates:
                    "text"            => $l_str_ReferenceText,

                    // used in standard layout W/O COMBINED FOOTNOTES:
                    "post_id"         => self::$a_int_PostId,
                    "container_id"    => self::$a_int_ReferenceContainerId,
                    "note_id"         => MCI_Footnotes_Convert::Index($l_int_FirstFootnoteIndex, MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_STR_FOOTNOTES_COUNTER_STYLE)),
                    "link-start"      => self::$a_str_LinkOpenTag,
                    "link-end"        => self::$a_str_LinkCloseTag,
                    "link-span"       => self::$a_str_LinkSpan,
                    "terminator"      => $l_str_Terminator,
                    "anchor-element"  => $l_str_FootnoteAnchorElement,
                    "hard-link"       => $l_str_HardLinkAddress,

                    // used in standard layout WITH COMBINED IDENTICALS TURNED ON:
                    "pointer"         => $l_bool_FlagCombined ? '' : ' pointer',
                    "event"           => $l_bool_FlagCombined ? '' : $l_str_BacklinkEvent,
                    "backlinks"       => $l_bool_FlagCombined ? $l_str_FootnoteBacklinks : $l_str_FootnoteReference,

                    // Legacy placeholders for use in legacy layout templates:
                    "arrow"           => $l_str_FootnoteArrow,
                    "index"           => $l_str_FootnoteId,
                )
            );

            $l_str_Body .= $l_obj_Template->getContent();

            // extra line breaks for page source readability:
            $l_str_Body .= "\r\n\r\n";

            $l_obj_Template->reload();

        }

        // call again for robustness when priority levels don’t match any longer:
        self::$a_int_ScrollOffset = intval(MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_INT_FOOTNOTES_SCROLL_OFFSET));

        // streamline:
        $l_bool_CollapseDefault = MCI_Footnotes_Convert::toBool(MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_BOOL_REFERENCE_CONTAINER_COLLAPSE));

        /**
         * Reference container label
         *
         * - Bugfix: Reference container: Label: set empty label to U+202F NNBSP for more robustness, thanks to @lukashuggenberg feedback.
         *
         * @since 2.4.0
         * @datetime 2021-01-04T0504+0100
         *
         * @reporter @lukashuggenberg
         *
         * Themes may drop-cap a first letter of initial paragraphs, like this label.
         * In case of empty label that would apply to the left half button character.
         * Hence the point in setting an empty label to U+202F NARROW NO-BREAK SPACE.
         */
        $l_str_ReferenceContainerLabel = MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_STR_REFERENCE_CONTAINER_NAME);

        // load 'templates/public/reference-container.html':
        $l_obj_TemplateContainer = new MCI_Footnotes_Template(MCI_Footnotes_Template::C_STR_PUBLIC, "reference-container");
        $l_obj_TemplateContainer->replace(
            array(
                "post_id"         =>  self::$a_int_PostId,
                "container_id"    =>  self::$a_int_ReferenceContainerId,
                "element"         =>  MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_STR_REFERENCE_CONTAINER_LABEL_ELEMENT),
                "name"            =>  empty($l_str_ReferenceContainerLabel) ? '&#x202F;' : $l_str_ReferenceContainerLabel,
                "button-style"    => !$l_bool_CollapseDefault ? 'display: none;' : '',
                "style"           =>  $l_bool_CollapseDefault ? 'display: none;' : '',
                "content"         =>  $l_str_Body,
                "scroll-offset"   =>  (self::$a_int_ScrollOffset / 100),
                "scroll-duration" =>  intval(MCI_Footnotes_Settings::instance()->get(MCI_Footnotes_Settings::C_INT_FOOTNOTES_SCROLL_DURATION)),
            )
        );

        // free all found footnotes if reference container will be displayed
        self::$a_arr_Footnotes = array();

        return $l_obj_TemplateContainer->getContent();
    }
}