showdownjs/src/subParsers/stripLinkDefinitions.js

/**
 * Strips link definitions from text, stores the URLs and titles in
 * hash references.
 * Link defs are in the form: ^[id]: url "optional title"
 *
 * ^[ ]{0,3}\[(.+)\]: // id = $1  attacklab: g_tab_width - 1
 * [ \t]*
 * \n?                  // maybe *one* newline
 * [ \t]*
 * <?(\S+?)>?          // url = $2
 * [ \t]*
 * \n?                // maybe one newline
 * [ \t]*
 * (?:
 * (\n*)              // any lines skipped = $3 attacklab: lookbehind removed
 * ["(]
 * (.+?)              // title = $4
 * [")]
 * [ \t]*
 * )?                 // title is optional
 * (?:\n+|$)
 * /gm,
 * function(){...});
 *
 */
showdown.subParser('stripLinkDefinitions', function (text, options, globals) {
  'use strict';

  var regex = /^[ ]{0,3}\[(.+)]:[ \t]*\n?[ \t]*<?(\S+?)>?[ \t]*\n?[ \t]*(?:(\n*)["(](.+?)[")][ \t]*)?(?:\n+|(?=~0))/gm;

  // attacklab: sentinel workarounds for lack of \A and \Z, safari\khtml bug
  text += '~0';

  text = text.replace(regex, function (wholeMatch, m1, m2, m3, m4) {
    m1 = m1.toLowerCase();
    globals.gUrls[m1] = showdown.subParser('encodeAmpsAndAngles')(m2);  // Link IDs are case-insensitive
    if (m3) {
      // Oops, found blank lines, so it's not a title.
      // Put back the parenthetical statement we stole.
      return m3 + m4;

    } else if (m4) {
      globals.gTitles[m1] = m4.replace(/"/g, '&quot;');
    }

    // Completely remove the definition from the text
    return '';
  });

  // attacklab: strip sentinel
  text = text.replace(/~0/, '');

  return text;
});