/bonfire/helpers/markdown_helper.php

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<?php

/**
 * Bonfire
 *
 * An open source project to allow developers to jumpstart their development of
 * CodeIgniter applications.
 *
 * @package   Bonfire
 * @author    Bonfire Dev Team
 * @copyright Copyright (c) 2011 - 2018, Bonfire Dev Team
 * @license   http://opensource.org/licenses/MIT The MIT License.
 * @link      http://cibonfire.com
 * @since     0.7.2
 * @filesource
 */

/**
 * Markdown Extra Helper
 *
 * @deprecated since 0.9.0. Use Bonfire's CommonMark library with one of the drivers
 * in /application/libraries/CommonMark/drivers/
 * @see https://github.com/ci-bonfire/Bonfire/blob/develop/bonfire/docs/commonmark.md
 *
 * This is here primarily for backwards compatibility, and has been updated only
 * because it should be kept up to date until it is removed.
 *
 * This is PHP Markdown / classic version
 * @link https://michelf.ca/projects/php-markdown/classic/
 *
 * @package Bonfire\Helpers\markdown_helper
 * @author  Bonfire Dev Team
 * @author  Michel Fortin
 * @author  John Gruber
 * @link    https://github.com/michelf/php-markdown/
 * @link    https://github.com/ci-bonfire/Bonfire/blob/develop/bonfire/docs/commonmark.md
 */

#
# Markdown Extra  -  A text-to-HTML conversion tool for web writers
#
# PHP Markdown & Extra
# Copyright (c) 2004-2013 Michel Fortin
# <http://michelf.ca/projects/php-markdown/>
#
# Original Markdown
# Copyright (c) 2004-2006 John Gruber
# <http://daringfireball.net/projects/markdown/>
#


define( 'MARKDOWN_VERSION',  "1.0.2" ); # 29 Nov 2013
define( 'MARKDOWNEXTRA_VERSION',  "1.2.8" ); # 29 Nov 2013


#
# Global default settings:
#

# Change to ">" for HTML output
@define( 'MARKDOWN_EMPTY_ELEMENT_SUFFIX',  " />");

# Define the width of a tab for code blocks.
@define( 'MARKDOWN_TAB_WIDTH',     4 );

# Optional title attribute for footnote links and backlinks.
@define( 'MARKDOWN_FN_LINK_TITLE',         "" );
@define( 'MARKDOWN_FN_BACKLINK_TITLE',     "" );

# Optional class attribute for footnote links and backlinks.
@define( 'MARKDOWN_FN_LINK_CLASS',         "" );
@define( 'MARKDOWN_FN_BACKLINK_CLASS',     "" );

# Optional class prefix for fenced code block.
@define( 'MARKDOWN_CODE_CLASS_PREFIX',     "" );

# Class attribute for code blocks goes on the `code` tag;
# setting this to true will put attributes on the `pre` tag instead.
@define( 'MARKDOWN_CODE_ATTR_ON_PRE',   false );


#
# WordPress settings:
#

# Change to false to remove Markdown from posts and/or comments.
@define( 'MARKDOWN_WP_POSTS',      true );
@define( 'MARKDOWN_WP_COMMENTS',   true );



### Standard Function Interface ###

@define( 'MARKDOWN_PARSER_CLASS',  'MarkdownExtra_Parser' );

function Markdown($text) {
#
# Initialize the parser and return the result of its transform method.
#
    # Setup static parser variable.
    static $parser;
    if (!isset($parser)) {
        $parser_class = MARKDOWN_PARSER_CLASS;
        $parser = new $parser_class;
    }

    # Transform text using parser.
    return $parser->transform($text);
}


### WordPress Plugin Interface ###

/*
Plugin Name: Markdown Extra
Plugin Name: Markdown
Plugin URI: http://michelf.ca/projects/php-markdown/
Description: <a href="http://daringfireball.net/projects/markdown/syntax">Markdown syntax</a> allows you to write using an easy-to-read, easy-to-write plain text format. Based on the original Perl version by <a href="http://daringfireball.net/">John Gruber</a>. <a href="http://michelf.ca/projects/php-markdown/">More...</a>
Version: 1.2.8
Author: Michel Fortin
Author URI: http://michelf.ca/
*/

if (isset($wp_version)) {
    # More details about how it works here:
    # <http://michelf.ca/weblog/2005/wordpress-text-flow-vs-markdown/>

    # Post content and excerpts
    # - Remove WordPress paragraph generator.
    # - Run Markdown on excerpt, then remove all tags.
    # - Add paragraph tag around the excerpt, but remove it for the excerpt rss.
    if (MARKDOWN_WP_POSTS) {
        remove_filter('the_content',     'wpautop');
        remove_filter('the_content_rss', 'wpautop');
        remove_filter('the_excerpt',     'wpautop');
        add_filter('the_content',     'mdwp_MarkdownPost', 6);
        add_filter('the_content_rss', 'mdwp_MarkdownPost', 6);
        add_filter('get_the_excerpt', 'mdwp_MarkdownPost', 6);
        add_filter('get_the_excerpt', 'trim', 7);
        add_filter('the_excerpt',     'mdwp_add_p');
        add_filter('the_excerpt_rss', 'mdwp_strip_p');

        remove_filter('content_save_pre',  'balanceTags', 50);
        remove_filter('excerpt_save_pre',  'balanceTags', 50);
        add_filter('the_content',     'balanceTags', 50);
        add_filter('get_the_excerpt', 'balanceTags', 9);
    }

    # Add a footnote id prefix to posts when inside a loop.
    function mdwp_MarkdownPost($text) {
        static $parser;
        if (!$parser) {
            $parser_class = MARKDOWN_PARSER_CLASS;
            $parser = new $parser_class;
        }
        if (is_single() || is_page() || is_feed()) {
            $parser->fn_id_prefix = "";
        } else {
            $parser->fn_id_prefix = get_the_ID() . ".";
        }
        return $parser->transform($text);
    }

    # Comments
    # - Remove WordPress paragraph generator.
    # - Remove WordPress auto-link generator.
    # - Scramble important tags before passing them to the kses filter.
    # - Run Markdown on excerpt then remove paragraph tags.
    if (MARKDOWN_WP_COMMENTS) {
        remove_filter('comment_text', 'wpautop', 30);
        remove_filter('comment_text', 'make_clickable');
        add_filter('pre_comment_content', 'Markdown', 6);
        add_filter('pre_comment_content', 'mdwp_hide_tags', 8);
        add_filter('pre_comment_content', 'mdwp_show_tags', 12);
        add_filter('get_comment_text',    'Markdown', 6);
        add_filter('get_comment_excerpt', 'Markdown', 6);
        add_filter('get_comment_excerpt', 'mdwp_strip_p', 7);

        global $mdwp_hidden_tags, $mdwp_placeholders;
        $mdwp_hidden_tags = explode(' ',
            '<p> </p> <pre> </pre> <ol> </ol> <ul> </ul> <li> </li>');
        $mdwp_placeholders = explode(' ', str_rot13(
            'pEj07ZbbBZ U1kqgh4w4p pre2zmeN6K QTi31t9pre ol0MP1jzJR '.
            'ML5IjmbRol ulANi1NsGY J7zRLJqPul liA8ctl16T K9nhooUHli'));
    }

    function mdwp_add_p($text) {
        if (!preg_match('{^$|^<(p|ul|ol|dl|pre|blockquote)>}i', $text)) {
            $text = '<p>'.$text.'</p>';
            $text = preg_replace('{\n{2,}}', "</p>\n\n<p>", $text);
        }
        return $text;
    }

    function mdwp_strip_p($t) { return preg_replace('{</?p>}i', '', $t); }

    function mdwp_hide_tags($text) {
        global $mdwp_hidden_tags, $mdwp_placeholders;
        return str_replace($mdwp_hidden_tags, $mdwp_placeholders, $text);
    }
    function mdwp_show_tags($text) {
        global $mdwp_hidden_tags, $mdwp_placeholders;
        return str_replace($mdwp_placeholders, $mdwp_hidden_tags, $text);
    }
}


### bBlog Plugin Info ###

function identify_modifier_markdown() {
    return array(
        'name' => 'markdown',
        'type' => 'modifier',
        'nicename' => 'PHP Markdown Extra',
        'description' => 'A text-to-HTML conversion tool for web writers',
        'authors' => 'Michel Fortin and John Gruber',
        'licence' => 'GPL',
        'version' => MARKDOWNEXTRA_VERSION,
        'help' => '<a href="http://daringfireball.net/projects/markdown/syntax">Markdown syntax</a> allows you to write using an easy-to-read, easy-to-write plain text format. Based on the original Perl version by <a href="http://daringfireball.net/">John Gruber</a>. <a href="http://michelf.ca/projects/php-markdown/">More...</a>',
        );
}


### Smarty Modifier Interface ###

function smarty_modifier_markdown($text) {
    return Markdown($text);
}


### Textile Compatibility Mode ###

# Rename this file to "classTextile.php" and it can replace Textile everywhere.

if (strcasecmp(substr(__FILE__, -16), "classTextile.php") == 0) {
    # Try to include PHP SmartyPants. Should be in the same directory.
    @include_once 'smartypants.php';
    # Fake Textile class. It calls Markdown instead.
    class Textile {
        function TextileThis($text, $lite='', $encode='') {
            if ($lite == '' && $encode == '')    $text = Markdown($text);
            if (function_exists('SmartyPants'))  $text = SmartyPants($text);
            return $text;
        }
        # Fake restricted version: restrictions are not supported for now.
        function TextileRestricted($text, $lite='', $noimage='') {
            return $this->TextileThis($text, $lite);
        }
        # Workaround to ensure compatibility with TextPattern 4.0.3.
        function blockLite($text) { return $text; }
    }
}



#
# Markdown Parser Class
#

class Markdown_Parser {

    ### Configuration Variables ###

    # Change to ">" for HTML output.
    var $empty_element_suffix = MARKDOWN_EMPTY_ELEMENT_SUFFIX;
    var $tab_width = MARKDOWN_TAB_WIDTH;

    # Change to `true` to disallow markup or entities.
    var $no_markup = false;
    var $no_entities = false;

    # Predefined urls and titles for reference links and images.
    var $predef_urls = array();
    var $predef_titles = array();


    ### Parser Implementation ###

    # Regex to match balanced [brackets].
    # Needed to insert a maximum bracked depth while converting to PHP.
    var $nested_brackets_depth = 6;
    var $nested_brackets_re;

    var $nested_url_parenthesis_depth = 4;
    var $nested_url_parenthesis_re;

    # Table of hash values for escaped characters:
    var $escape_chars = '\`*_{}[]()>#+-.!';
    var $escape_chars_re;


    function __construct() {
    #
    # Constructor function. Initialize appropriate member variables.
    #
        $this->_initDetab();
        $this->prepareItalicsAndBold();

        $this->nested_brackets_re =
            str_repeat('(?>[^\[\]]+|\[', $this->nested_brackets_depth).
            str_repeat('\])*', $this->nested_brackets_depth);

        $this->nested_url_parenthesis_re =
            str_repeat('(?>[^()\s]+|\(', $this->nested_url_parenthesis_depth).
            str_repeat('(?>\)))*', $this->nested_url_parenthesis_depth);

        $this->escape_chars_re = '['.preg_quote($this->escape_chars).']';

        # Sort document, block, and span gamut in ascendent priority order.
        asort($this->document_gamut);
        asort($this->block_gamut);
        asort($this->span_gamut);
    }


    # Internal hashes used during transformation.
    var $urls = array();
    var $titles = array();
    var $html_hashes = array();

    # Status flag to avoid invalid nesting.
    var $in_anchor = false;


    function setup() {
    #
    # Called before the transformation process starts to setup parser
    # states.
    #
        # Clear global hashes.
        $this->urls = $this->predef_urls;
        $this->titles = $this->predef_titles;
        $this->html_hashes = array();

        $this->in_anchor = false;
    }

    function teardown() {
    #
    # Called after the transformation process to clear any variable
    # which may be taking up memory unnecessarly.
    #
        $this->urls = array();
        $this->titles = array();
        $this->html_hashes = array();
    }


    function transform($text) {
    #
    # Main function. Performs some preprocessing on the input text
    # and pass it through the document gamut.
    #
        $this->setup();

        # Remove UTF-8 BOM and marker character in input, if present.
        $text = preg_replace('{^\xEF\xBB\xBF|\x1A}', '', $text);

        # Standardize line endings:
        #   DOS to Unix and Mac to Unix
        $text = preg_replace('{\r\n?}', "\n", $text);

        # Make sure $text ends with a couple of newlines:
        $text .= "\n\n";

        # Convert all tabs to spaces.
        $text = $this->detab($text);

        # Turn block-level HTML blocks into hash entries
        $text = $this->hashHTMLBlocks($text);

        # Strip any lines consisting only of spaces and tabs.
        # This makes subsequent regexen easier to write, because we can
        # match consecutive blank lines with /\n+/ instead of something
        # contorted like /[ ]*\n+/ .
        $text = preg_replace('/^[ ]+$/m', '', $text);

        # Run document gamut methods.
        foreach ($this->document_gamut as $method => $priority) {
            $text = $this->$method($text);
        }

        $this->teardown();

        return $text . "\n";
    }

    var $document_gamut = array(
        # Strip link definitions, store in hashes.
        "stripLinkDefinitions" => 20,

        "runBasicBlockGamut"   => 30,
        );


    function stripLinkDefinitions($text) {
    #
    # Strips link definitions from text, stores the URLs and titles in
    # hash references.
    #
        $less_than_tab = $this->tab_width - 1;

        # Link defs are in the form: ^[id]: url "optional title"
        $text = preg_replace_callback('{
                            ^[ ]{0,'.$less_than_tab.'}\[(.+)\][ ]?: # id = $1
                              [ ]*
                              \n?               # maybe *one* newline
                              [ ]*
                            (?:
                              <(.+?)>           # url = $2
                            |
                              (\S+?)            # url = $3
                            )
                              [ ]*
                              \n?               # maybe one newline
                              [ ]*
                            (?:
                                (?<=\s)         # lookbehind for whitespace
                                ["(]
                                (.*?)           # title = $4
                                [")]
                                [ ]*
                            )?  # title is optional
                            (?:\n+|\Z)
            }xm',
            array(&$this, '_stripLinkDefinitions_callback'),
            $text);
        return $text;
    }
    function _stripLinkDefinitions_callback($matches) {
        $link_id = strtolower($matches[1]);
        $url = $matches[2] == '' ? $matches[3] : $matches[2];
        $this->urls[$link_id] = $url;
        $this->titles[$link_id] =& $matches[4];
        return ''; # String that will replace the block
    }


    function hashHTMLBlocks($text) {
        if ($this->no_markup)  return $text;

        $less_than_tab = $this->tab_width - 1;

        # Hashify HTML blocks:
        # We only want to do this for block-level HTML tags, such as headers,
        # lists, and tables. That's because we still want to wrap <p>s around
        # "paragraphs" that are wrapped in non-block-level tags, such as anchors,
        # phrase emphasis, and spans. The list of tags we're looking for is
        # hard-coded:
        #
        # *  List "a" is made of tags which can be both inline or block-level.
        #    These will be treated block-level when the start tag is alone on
        #    its line, otherwise they're not matched here and will be taken as
        #    inline later.
        # *  List "b" is made of tags which are always block-level;
        #
        $block_tags_a_re = 'ins|del';
        $block_tags_b_re = 'p|div|h[1-6]|blockquote|pre|table|dl|ol|ul|address|'.
                           'script|noscript|form|fieldset|iframe|math|svg|'.
                           'article|section|nav|aside|hgroup|header|footer|'.
                           'figure';

        # Regular expression for the content of a block tag.
        $nested_tags_level = 4;
        $attr = '
            (?>             # optional tag attributes
              \s            # starts with whitespace
              (?>
                [^>"/]+     # text outside quotes
              |
                /+(?!>)     # slash not followed by ">"
              |
                "[^"]*"     # text inside double quotes (tolerate ">")
              |
                \'[^\']*\'  # text inside single quotes (tolerate ">")
              )*
            )?
            ';
        $content =
            str_repeat('
                (?>
                  [^<]+         # content without tag
                |
                  <\2           # nested opening tag
                    '.$attr.'   # attributes
                    (?>
                      />
                    |
                      >', $nested_tags_level).  # end of opening tag
                      '.*?'.                    # last level nested tag content
            str_repeat('
                      </\2\s*>  # closing nested tag
                    )
                  |
                    <(?!/\2\s*> # other tags with a different name
                  )
                )*',
                $nested_tags_level);
        $content2 = str_replace('\2', '\3', $content);

        # First, look for nested blocks, e.g.:
        #   <div>
        #       <div>
        #       tags for inner block must be indented.
        #       </div>
        #   </div>
        #
        # The outermost tags must start at the left margin for this to match, and
        # the inner nested divs must be indented.
        # We need to do this before the next, more liberal match, because the next
        # match will start at the first `<div>` and stop at the first `</div>`.
        $text = preg_replace_callback('{(?>
            (?>
                (?<=\n\n)       # Starting after a blank line
                |               # or
                \A\n?           # the beginning of the doc
            )
            (                       # save in $1

              # Match from `\n<tag>` to `</tag>\n`, handling nested tags
              # in between.

                        [ ]{0,'.$less_than_tab.'}
                        <('.$block_tags_b_re.')# start tag = $2
                        '.$attr.'>          # attributes followed by > and \n
                        '.$content.'        # content, support nesting
                        </\2>               # the matching end tag
                        [ ]*                # trailing spaces/tabs
                        (?=\n+|\Z)  # followed by a newline or end of document

            | # Special version for tags of group a.

                        [ ]{0,'.$less_than_tab.'}
                        <('.$block_tags_a_re.')# start tag = $3
                        '.$attr.'>[ ]*\n    # attributes followed by >
                        '.$content2.'       # content, support nesting
                        </\3>               # the matching end tag
                        [ ]*                # trailing spaces/tabs
                        (?=\n+|\Z)  # followed by a newline or end of document

            | # Special case just for <hr />. It was easier to make a special
              # case than to make the other regex more complicated.

                        [ ]{0,'.$less_than_tab.'}
                        <(hr)               # start tag = $2
                        '.$attr.'           # attributes
                        /?>                 # the matching end tag
                        [ ]*
                        (?=\n{2,}|\Z)       # followed by a blank line or end of document

            | # Special case for standalone HTML comments:

                    [ ]{0,'.$less_than_tab.'}
                    (?s:
                        <!-- .*? -->
                    )
                    [ ]*
                    (?=\n{2,}|\Z)       # followed by a blank line or end of document

            | # PHP and ASP-style processor instructions (<? and <%)

                    [ ]{0,'.$less_than_tab.'}
                    (?s:
                        <([?%])         # $2
                        .*?
                        \2>
                    )
                    [ ]*
                    (?=\n{2,}|\Z)       # followed by a blank line or end of document

            )
            )}Sxmi',
            array(&$this, '_hashHTMLBlocks_callback'),
            $text);

        return $text;
    }
    function _hashHTMLBlocks_callback($matches) {
        $text = $matches[1];
        $key  = $this->hashBlock($text);
        return "\n\n$key\n\n";
    }


    function hashPart($text, $boundary = 'X') {
    #
    # Called whenever a tag must be hashed when a function insert an atomic
    # element in the text stream. Passing $text to through this function gives
    # a unique text-token which will be reverted back when calling unhash.
    #
    # The $boundary argument specify what character should be used to surround
    # the token. By convension, "B" is used for block elements that needs not
    # to be wrapped into paragraph tags at the end, ":" is used for elements
    # that are word separators and "X" is used in the general case.
    #
        # Swap back any tag hash found in $text so we do not have to `unhash`
        # multiple times at the end.
        $text = $this->unhash($text);

        # Then hash the block.
        static $i = 0;
        $key = "$boundary\x1A" . ++$i . $boundary;
        $this->html_hashes[$key] = $text;
        return $key; # String that will replace the tag.
    }


    function hashBlock($text) {
    #
    # Shortcut function for hashPart with block-level boundaries.
    #
        return $this->hashPart($text, 'B');
    }


    var $block_gamut = array(
    #
    # These are all the transformations that form block-level
    # tags like paragraphs, headers, and list items.
    #
        "doHeaders"         => 10,
        "doHorizontalRules" => 20,

        "doLists"           => 40,
        "doCodeBlocks"      => 50,
        "doBlockQuotes"     => 60,
        );

    function runBlockGamut($text) {
    #
    # Run block gamut tranformations.
    #
        # We need to escape raw HTML in Markdown source before doing anything
        # else. This need to be done for each block, and not only at the
        # begining in the Markdown function since hashed blocks can be part of
        # list items and could have been indented. Indented blocks would have
        # been seen as a code block in a previous pass of hashHTMLBlocks.
        $text = $this->hashHTMLBlocks($text);

        return $this->runBasicBlockGamut($text);
    }

    function runBasicBlockGamut($text) {
    #
    # Run block gamut tranformations, without hashing HTML blocks. This is
    # useful when HTML blocks are known to be already hashed, like in the first
    # whole-document pass.
    #
        foreach ($this->block_gamut as $method => $priority) {
            $text = $this->$method($text);
        }

        # Finally form paragraph and restore hashed blocks.
        $text = $this->formParagraphs($text);

        return $text;
    }


    function doHorizontalRules($text) {
        # Do Horizontal Rules:
        return preg_replace(
            '{
                ^[ ]{0,3}   # Leading space
                ([-*_])     # $1: First marker
                (?>         # Repeated marker group
                    [ ]{0,2}    # Zero, one, or two spaces.
                    \1          # Marker character
                ){2,}       # Group repeated at least twice
                [ ]*        # Tailing spaces
                $           # End of line.
            }mx',
            "\n".$this->hashBlock("<hr$this->empty_element_suffix")."\n",
            $text);
    }


    var $span_gamut = array(
    #
    # These are all the transformations that occur *within* block-level
    # tags like paragraphs, headers, and list items.
    #
        # Process character escapes, code spans, and inline HTML
        # in one shot.
        "parseSpan"           => -30,

        # Process anchor and image tags. Images must come first,
        # because ![foo][f] looks like an anchor.
        "doImages"            =>  10,
        "doAnchors"           =>  20,

        # Make links out of things like `<http://example.com/>`
        # Must come after doAnchors, because you can use < and >
        # delimiters in inline links like [this](<url>).
        "doAutoLinks"         =>  30,
        "encodeAmpsAndAngles" =>  40,

        "doItalicsAndBold"    =>  50,
        "doHardBreaks"        =>  60,
        );

    function runSpanGamut($text) {
    #
    # Run span gamut tranformations.
    #
        foreach ($this->span_gamut as $method => $priority) {
            $text = $this->$method($text);
        }

        return $text;
    }


    function doHardBreaks($text) {
        # Do hard breaks:
        return preg_replace_callback('/ {2,}\n/',
            array(&$this, '_doHardBreaks_callback'), $text);
    }
    function _doHardBreaks_callback($matches) {
        return $this->hashPart("<br$this->empty_element_suffix\n");
    }


    function doAnchors($text) {
    #
    # Turn Markdown link shortcuts into XHTML <a> tags.
    #
        if ($this->in_anchor) return $text;
        $this->in_anchor = true;

        #
        # First, handle reference-style links: [link text] [id]
        #
        $text = preg_replace_callback('{
            (                   # wrap whole match in $1
              \[
                ('.$this->nested_brackets_re.') # link text = $2
              \]

              [ ]?              # one optional space
              (?:\n[ ]*)?       # one optional newline followed by spaces

              \[
                (.*?)       # id = $3
              \]
            )
            }xs',
            array(&$this, '_doAnchors_reference_callback'), $text);

        #
        # Next, inline-style links: [link text](url "optional title")
        #
        $text = preg_replace_callback('{
            (               # wrap whole match in $1
              \[
                ('.$this->nested_brackets_re.') # link text = $2
              \]
              \(            # literal paren
                [ \n]*
                (?:
                    <(.+?)> # href = $3
                |
                    ('.$this->nested_url_parenthesis_re.')  # href = $4
                )
                [ \n]*
                (           # $5
                  ([\'"])   # quote char = $6
                  (.*?)     # Title = $7
                  \6        # matching quote
                  [ \n]*    # ignore any spaces/tabs between closing quote and )
                )?          # title is optional
              \)
            )
            }xs',
            array(&$this, '_doAnchors_inline_callback'), $text);

        #
        # Last, handle reference-style shortcuts: [link text]
        # These must come last in case you've also got [link text][1]
        # or [link text](/foo)
        #
        $text = preg_replace_callback('{
            (                   # wrap whole match in $1
              \[
                ([^\[\]]+)      # link text = $2; can\'t contain [ or ]
              \]
            )
            }xs',
            array(&$this, '_doAnchors_reference_callback'), $text);

        $this->in_anchor = false;
        return $text;
    }
    function _doAnchors_reference_callback($matches) {
        $whole_match =  $matches[1];
        $link_text   =  $matches[2];
        $link_id     =& $matches[3];

        if ($link_id == "") {
            # for shortcut links like [this][] or [this].
            $link_id = $link_text;
        }

        # lower-case and turn embedded newlines into spaces
        $link_id = strtolower($link_id);
        $link_id = preg_replace('{[ ]?\n}', ' ', $link_id);

        if (isset($this->urls[$link_id])) {
            $url = $this->urls[$link_id];
            $url = $this->encodeAttribute($url);

            $result = "<a href=\"$url\"";
            if ( isset( $this->titles[$link_id] ) ) {
                $title = $this->titles[$link_id];
                $title = $this->encodeAttribute($title);
                $result .=  " title=\"$title\"";
            }

            $link_text = $this->runSpanGamut($link_text);
            $result .= ">$link_text</a>";
            $result = $this->hashPart($result);
        }
        else {
            $result = $whole_match;
        }
        return $result;
    }
    function _doAnchors_inline_callback($matches) {
        $whole_match    =  $matches[1];
        $link_text      =  $this->runSpanGamut($matches[2]);
        $url            =  $matches[3] == '' ? $matches[4] : $matches[3];
        $title          =& $matches[7];

        $url = $this->encodeAttribute($url);

        $result = "<a href=\"$url\"";
        if (isset($title)) {
            $title = $this->encodeAttribute($title);
            $result .=  " title=\"$title\"";
        }

        $link_text = $this->runSpanGamut($link_text);
        $result .= ">$link_text</a>";

        return $this->hashPart($result);
    }


    function doImages($text) {
    #
    # Turn Markdown image shortcuts into <img> tags.
    #
        #
        # First, handle reference-style labeled images: ![alt text][id]
        #
        $text = preg_replace_callback('{
            (               # wrap whole match in $1
              !\[
                ('.$this->nested_brackets_re.')     # alt text = $2
              \]

              [ ]?              # one optional space
              (?:\n[ ]*)?       # one optional newline followed by spaces

              \[
                (.*?)       # id = $3
              \]

            )
            }xs',
            array(&$this, '_doImages_reference_callback'), $text);

        #
        # Next, handle inline images:  ![alt text](url "optional title")
        # Don't forget: encode * and _
        #
        $text = preg_replace_callback('{
            (               # wrap whole match in $1
              !\[
                ('.$this->nested_brackets_re.')     # alt text = $2
              \]
              \s?           # One optional whitespace character
              \(            # literal paren
                [ \n]*
                (?:
                    <(\S*)> # src url = $3
                |
                    ('.$this->nested_url_parenthesis_re.')  # src url = $4
                )
                [ \n]*
                (           # $5
                  ([\'"])   # quote char = $6
                  (.*?)     # title = $7
                  \6        # matching quote
                  [ \n]*
                )?          # title is optional
              \)
            )
            }xs',
            array(&$this, '_doImages_inline_callback'), $text);

        return $text;
    }
    function _doImages_reference_callback($matches) {
        $whole_match = $matches[1];
        $alt_text    = $matches[2];
        $link_id     = strtolower($matches[3]);

        if ($link_id == "") {
            $link_id = strtolower($alt_text); # for shortcut links like ![this][].
        }

        $alt_text = $this->encodeAttribute($alt_text);
        if (isset($this->urls[$link_id])) {
            $url = $this->encodeAttribute($this->urls[$link_id]);
            $result = "<img src=\"$url\" alt=\"$alt_text\"";
            if (isset($this->titles[$link_id])) {
                $title = $this->titles[$link_id];
                $title = $this->encodeAttribute($title);
                $result .=  " title=\"$title\"";
            }
            $result .= $this->empty_element_suffix;
            $result = $this->hashPart($result);
        }
        else {
            # If there's no such link ID, leave intact:
            $result = $whole_match;
        }

        return $result;
    }
    function _doImages_inline_callback($matches) {
        $whole_match    = $matches[1];
        $alt_text       = $matches[2];
        $url            = $matches[3] == '' ? $matches[4] : $matches[3];
        $title          =& $matches[7];

        $alt_text = $this->encodeAttribute($alt_text);
        $url = $this->encodeAttribute($url);
        $result = "<img src=\"$url\" alt=\"$alt_text\"";
        if (isset($title)) {
            $title = $this->encodeAttribute($title);
            $result .=  " title=\"$title\""; # $title already quoted
        }
        $result .= $this->empty_element_suffix;

        return $this->hashPart($result);
    }


    function doHeaders($text) {
        # Setext-style headers:
        #     Header 1
        #     ========
        #
        #     Header 2
        #     --------
        #
        $text = preg_replace_callback('{ ^(.+?)[ ]*\n(=+|-+)[ ]*\n+ }mx',
            array(&$this, '_doHeaders_callback_setext'), $text);

        # atx-style headers:
        #   # Header 1
        #   ## Header 2
        #   ## Header 2 with closing hashes ##
        #   ...
        #   ###### Header 6
        #
        $text = preg_replace_callback('{
                ^(\#{1,6})  # $1 = string of #\'s
                [ ]*
                (.+?)       # $2 = Header text
                [ ]*
                \#*         # optional closing #\'s (not counted)
                \n+
            }xm',
            array(&$this, '_doHeaders_callback_atx'), $text);

        return $text;
    }
    function _doHeaders_callback_setext($matches) {
        # Terrible hack to check we haven't found an empty list item.
        if ($matches[2] == '-' && preg_match('{^-(?: |$)}', $matches[1]))
            return $matches[0];

        $level = $matches[2]{0} == '=' ? 1 : 2;
        $block = "<h$level>".$this->runSpanGamut($matches[1])."</h$level>";
        return "\n" . $this->hashBlock($block) . "\n\n";
    }
    function _doHeaders_callback_atx($matches) {
        $level = strlen($matches[1]);
        $block = "<h$level>".$this->runSpanGamut($matches[2])."</h$level>";
        return "\n" . $this->hashBlock($block) . "\n\n";
    }


    function doLists($text) {
    #
    # Form HTML ordered (numbered) and unordered (bulleted) lists.
    #
        $less_than_tab = $this->tab_width - 1;

        # Re-usable patterns to match list item bullets and number markers:
        $marker_ul_re  = '[*+-]';
        $marker_ol_re  = '\d+[\.]';
        $marker_any_re = "(?:$marker_ul_re|$marker_ol_re)";

        $markers_relist = array(
            $marker_ul_re => $marker_ol_re,
            $marker_ol_re => $marker_ul_re,
            );

        foreach ($markers_relist as $marker_re => $other_marker_re) {
            # Re-usable pattern to match any entirel ul or ol list:
            $whole_list_re = '
                (                               # $1 = whole list
                  (                             # $2
                    ([ ]{0,'.$less_than_tab.'}) # $3 = number of spaces
                    ('.$marker_re.')            # $4 = first list item marker
                    [ ]+
                  )
                  (?s:.+?)
                  (                             # $5
                      \z
                    |
                      \n{2,}
                      (?=\S)
                      (?!                       # Negative lookahead for another list item marker
                        [ ]*
                        '.$marker_re.'[ ]+
                      )
                    |
                      (?=                       # Lookahead for another kind of list
                        \n
                        \3                      # Must have the same indentation
                        '.$other_marker_re.'[ ]+
                      )
                  )
                )
            '; // mx

            # We use a different prefix before nested lists than top-level lists.
            # See extended comment in _ProcessListItems().

            if ($this->list_level) {
                $text = preg_replace_callback('{
                        ^
                        '.$whole_list_re.'
                    }mx',
                    array(&$this, '_doLists_callback'), $text);
            }
            else {
                $text = preg_replace_callback('{
                        (?:(?<=\n)\n|\A\n?) # Must eat the newline
                        '.$whole_list_re.'
                    }mx',
                    array(&$this, '_doLists_callback'), $text);
            }
        }

        return $text;
    }
    function _doLists_callback($matches) {
        # Re-usable patterns to match list item bullets and number markers:
        $marker_ul_re  = '[*+-]';
        $marker_ol_re  = '\d+[\.]';
        $marker_any_re = "(?:$marker_ul_re|$marker_ol_re)";

        $list = $matches[1];
        $list_type = preg_match("/$marker_ul_re/", $matches[4]) ? "ul" : "ol";

        $marker_any_re = ( $list_type == "ul" ? $marker_ul_re : $marker_ol_re );

        $list .= "\n";
        $result = $this->processListItems($list, $marker_any_re);

        $result = $this->hashBlock("<$list_type>\n" . $result . "</$list_type>");
        return "\n". $result ."\n\n";
    }

    var $list_level = 0;

    function processListItems($list_str, $marker_any_re) {
    #
    #   Process the contents of a single ordered or unordered list, splitting it
    #   into individual list items.
    #
        # The $this->list_level global keeps track of when we're inside a list.
        # Each time we enter a list, we increment it; when we leave a list,
        # we decrement. If it's zero, we're not in a list anymore.
        #
        # We do this because when we're not inside a list, we want to treat
        # something like this:
        #
        #       I recommend upgrading to version
        #       8. Oops, now this line is treated
        #       as a sub-list.
        #
        # As a single paragraph, despite the fact that the second line starts
        # with a digit-period-space sequence.
        #
        # Whereas when we're inside a list (or sub-list), that line will be
        # treated as the start of a sub-list. What a kludge, huh? This is
        # an aspect of Markdown's syntax that's hard to parse perfectly
        # without resorting to mind-reading. Perhaps the solution is to
        # change the syntax rules such that sub-lists must start with a
        # starting cardinal number; e.g. "1." or "a.".

        $this->list_level++;

        # trim trailing blank lines:
        $list_str = preg_replace("/\n{2,}\\z/", "\n", $list_str);

        $list_str = preg_replace_callback('{
            (\n)?                           # leading line = $1
            (^[ ]*)                         # leading whitespace = $2
            ('.$marker_any_re.'             # list marker and space = $3
                (?:[ ]+|(?=\n)) # space only required if item is not empty
            )
            ((?s:.*?))                      # list item text   = $4
            (?:(\n+(?=\n))|\n)              # tailing blank line = $5
            (?= \n* (\z | \2 ('.$marker_any_re.') (?:[ ]+|(?=\n))))
            }xm',
            array(&$this, '_processListItems_callback'), $list_str);

        $this->list_level--;
        return $list_str;
    }
    function _processListItems_callback($matches) {
        $item = $matches[4];
        $leading_line =& $matches[1];
        $leading_space =& $matches[2];
        $marker_space = $matches[3];
        $tailing_blank_line =& $matches[5];

        if ($leading_line || $tailing_blank_line ||
            preg_match('/\n{2,}/', $item))
        {
            # Replace marker with the appropriate whitespace indentation
            $item = $leading_space . str_repeat(' ', strlen($marker_space)) . $item;
            $item = $this->runBlockGamut($this->outdent($item)."\n");
        }
        else {
            # Recursion for sub-lists:
            $item = $this->doLists($this->outdent($item));
            $item = preg_replace('/\n+$/', '', $item);
            $item = $this->runSpanGamut($item);
        }

        return "<li>" . $item . "</li>\n";
    }


    function doCodeBlocks($text) {
    #
    #   Process Markdown `<pre><code>` blocks.
    #
        $text = preg_replace_callback('{
                (?:\n\n|\A\n?)
                (               # $1 = the code block -- one or more lines, starting with a space/tab
                  (?>
                    [ ]{'.$this->tab_width.'}  # Lines must start with a tab or a tab-width of spaces
                    .*\n+
                  )+
                )
                ((?=^[ ]{0,'.$this->tab_width.'}\S)|\Z) # Lookahead for non-space at line-start, or end of doc
            }xm',
            array(&$this, '_doCodeBlocks_callback'), $text);

        return $text;
    }
    function _doCodeBlocks_callback($matches) {
        $codeblock = $matches[1];

        $codeblock = $this->outdent($codeblock);
        $codeblock = htmlspecialchars($codeblock, ENT_NOQUOTES);

        # trim leading newlines and trailing newlines
        $codeblock = preg_replace('/\A\n+|\n+\z/', '', $codeblock);

        $codeblock = "<pre><code>$codeblock\n</code></pre>";
        return "\n\n".$this->hashBlock($codeblock)."\n\n";
    }


    function makeCodeSpan($code) {
    #
    # Create a code span markup for $code. Called from handleSpanToken.
    #
        $code = htmlspecialchars(trim($code), ENT_NOQUOTES);
        return $this->hashPart("<code>$code</code>");
    }


    var $em_relist = array(
        ''  => '(?:(?<!\*)\*(?!\*)|(?<!_)_(?!_))(?=\S|$)(?![\.,:;]\s)',
        '*' => '(?<=\S|^)(?<!\*)\*(?!\*)',
        '_' => '(?<=\S|^)(?<!_)_(?!_)',
        );
    var $strong_relist = array(
        ''   => '(?:(?<!\*)\*\*(?!\*)|(?<!_)__(?!_))(?=\S|$)(?![\.,:;]\s)',
        '**' => '(?<=\S|^)(?<!\*)\*\*(?!\*)',
        '__' => '(?<=\S|^)(?<!_)__(?!_)',
        );
    var $em_strong_relist = array(
        ''    => '(?:(?<!\*)\*\*\*(?!\*)|(?<!_)___(?!_))(?=\S|$)(?![\.,:;]\s)',
        '***' => '(?<=\S|^)(?<!\*)\*\*\*(?!\*)',
        '___' => '(?<=\S|^)(?<!_)___(?!_)',
        );
    var $em_strong_prepared_relist;

    function prepareItalicsAndBold() {
    #
    # Prepare regular expressions for searching emphasis tokens in any
    # context.
    #
        foreach ($this->em_relist as $em => $em_re) {
            foreach ($this->strong_relist as $strong => $strong_re) {
                # Construct list of allowed token expressions.
                $token_relist = array();
                if (isset($this->em_strong_relist["$em$strong"])) {
                    $token_relist[] = $this->em_strong_relist["$em$strong"];
                }
                $token_relist[] = $em_re;
                $token_relist[] = $strong_re;

                # Construct master expression from list.
                $token_re = '{('. implode('|', $token_relist) .')}';
                $this->em_strong_prepared_relist["$em$strong"] = $token_re;
            }
        }
    }

    function doItalicsAndBold($text) {
        $token_stack = array('');
        $text_stack = array('');
        $em = '';
        $strong = '';
        $tree_char_em = false;

        while (1) {
            #
            # Get prepared regular expression for seraching emphasis tokens
            # in current context.
            #
            $token_re = $this->em_strong_prepared_relist["$em$strong"];

            #
            # Each loop iteration search for the next emphasis token.
            # Each token is then passed to handleSpanToken.
            #
            $parts = preg_split($token_re, $text, 2, PREG_SPLIT_DELIM_CAPTURE);
            $text_stack[0] .= $parts[0];
            $token =& $parts[1];
            $text =& $parts[2];

            if (empty($token)) {
                # Reached end of text span: empty stack without emitting.
                # any more emphasis.
                while ($token_stack[0]) {
                    $text_stack[1] .= array_shift($token_stack);
                    $text_stack[0] .= array_shift($text_stack);
                }
                break;
            }

            $token_len = strlen($token);
            if ($tree_char_em) {
                # Reached closing marker while inside a three-char emphasis.
                if ($token_len == 3) {
                    # Three-char closing marker, close em and strong.
                    array_shift($token_stack);
                    $span = array_shift($text_stack);
                    $span = $this->runSpanGamut($span);
                    $span = "<strong><em>$span</em></strong>";
                    $text_stack[0] .= $this->hashPart($span);
                    $em = '';
                    $strong = '';
                } else {
                    # Other closing marker: close one em or strong and
                    # change current token state to match the other
                    $token_stack[0] = str_repeat($token{0}, 3-$token_len);
                    $tag = $token_len == 2 ? "strong" : "em";
                    $span = $text_stack[0];
                    $span = $this->runSpanGamut($span);
                    $span = "<$tag>$span</$tag>";
                    $text_stack[0] = $this->hashPart($span);
                    $$tag = ''; # $$tag stands for $em or $strong
                }
                $tree_char_em = false;
            } else if ($token_len == 3) {
                if ($em) {
                    # Reached closing marker for both em and strong.
                    # Closing strong marker:
                    for ($i = 0; $i < 2; ++$i) {
                        $shifted_token = array_shift($token_stack);
                        $tag = strlen($shifted_token) == 2 ? "strong" : "em";
                        $span = array_shift($text_stack);
                        $span = $this->runSpanGamut($span);
                        $span = "<$tag>$span</$tag>";
                        $text_stack[0] .= $this->hashPart($span);
                        $$tag = ''; # $$tag stands for $em or $strong
                    }
                } else {
                    # Reached opening three-char emphasis marker. Push on token
                    # stack; will be handled by the special condition above.
                    $em = $token{0};
                    $strong = "$em$em";
                    array_unshift($token_stack, $token);
                    array_unshift($text_stack, '');
                    $tree_char_em = true;
                }
            } else if ($token_len == 2) {
                if ($strong) {
                    # Unwind any dangling emphasis marker:
                    if (strlen($token_stack[0]) == 1) {
                        $text_stack[1] .= array_shift($token_stack);
                        $text_stack[0] .= array_shift($text_stack);
                    }
                    # Closing strong marker:
                    array_shift($token_stack);
                    $span = array_shift($text_stack);
                    $span = $this->runSpanGamut($span);
                    $span = "<strong>$span</strong>";
                    $text_stack[0] .= $this->hashPart($span);
                    $strong = '';
                } else {
                    array_unshift($token_stack, $token);
                    array_unshift($text_stack, '');
                    $strong = $token;
                }
            } else {
                # Here $token_len == 1
                if ($em) {
                    if (strlen($token_stack[0]) == 1) {
                        # Closing emphasis marker:
                        array_shift($token_stack);
                        $span = array_shift($text_stack);
                        $span = $this->runSpanGamut($span);
                        $span = "<em>$span</em>";
                        $text_stack[0] .= $this->hashPart($span);
                        $em = '';
                    } else {
                        $text_stack[0] .= $token;
                    }
                } else {
                    array_unshift($token_stack, $token);
                    array_unshift($text_stack, '');
                    $em = $token;
                }
            }
        }
        return $text_stack[0];
    }


    function doBlockQuotes($text) {
        $text = preg_replace_callback('/
              (                             # Wrap whole match in $1
                (?>
                  ^[ ]*>[ ]?            # ">" at the start of a line
                    .+\n                    # rest of the first line
                  (.+\n)*                   # subsequent consecutive lines
                  \n*                       # blanks
                )+
              )
            /xm',
            array(&$this, '_doBlockQuotes_callback'), $text);

        return $text;
    }
    function _doBlockQuotes_callback($matches) {
        $bq = $matches[1];
        # trim one level of quoting - trim whitespace-only lines
        $bq = preg_replace('/^[ ]*>[ ]?|^[ ]+$/m', '', $bq);
        $bq = $this->runBlockGamut($bq);        # recurse

        $bq = preg_replace('/^/m', "  ", $bq);
        # These leading spaces cause problem with <pre> content,
        # so we need to fix that:
        $bq = preg_replace_callback('{(\s*<pre>.+?</pre>)}sx',
            array(&$this, '_doBlockQuotes_callback2'), $bq);

        return "\n". $this->hashBlock("<blockquote>\n$bq\n</blockquote>")."\n\n";
    }
    function _doBlockQuotes_callback2($matches) {
        $pre = $matches[1];
        $pre = preg_replace('/^  /m', '', $pre);
        return $pre;
    }


    function formParagraphs($text) {
    #
    #   Params:
    #       $text - string to process with html <p> tags
    #
        # Strip leading and trailing lines:
        $text = preg_replace('/\A\n+|\n+\z/', '', $text);

        $grafs = preg_split('/\n{2,}/', $text, -1, PREG_SPLIT_NO_EMPTY);

        #
        # Wrap <p> tags and unhashify HTML blocks
        #
        foreach ($grafs as $key => $value) {
            if (!preg_match('/^B\x1A[0-9]+B$/', $value)) {
                # Is a paragraph.
                $value = $this->runSpanGamut($value);
                $value = preg_replace('/^([ ]*)/', "<p>", $value);
                $value .= "</p>";
                $grafs[$key] = $this->unhash($value);
            }
            else {
                # Is a block.
                # Modify elements of @grafs in-place..…