app/node_modules/markdown-it-abbr/index.js

// Enclose abbreviations in <abbr> tags
//
'use strict';


module.exports = function sub_plugin(md) {
  var escapeRE        = md.utils.escapeRE,
      arrayReplaceAt  = md.utils.arrayReplaceAt;

  // ASCII characters in Cc, Sc, Sm, Sk categories we should terminate on;
  // you can check character classes here:
  // http://www.unicode.org/Public/UNIDATA/UnicodeData.txt
  var OTHER_CHARS      = ' \r\n$+<=>^`|~';

  var UNICODE_PUNCT_RE = md.utils.lib.ucmicro.P.source;
  var UNICODE_SPACE_RE = md.utils.lib.ucmicro.Z.source;


  function abbr_def(state, startLine, endLine, silent) {
    var label, title, ch, labelStart, labelEnd,
        pos = state.bMarks[startLine] + state.tShift[startLine],
        max = state.eMarks[startLine];

    if (pos + 2 >= max) { return false; }

    if (state.src.charCodeAt(pos++) !== 0x2A/* * */) { return false; }
    if (state.src.charCodeAt(pos++) !== 0x5B/* [ */) { return false; }

    labelStart = pos;

    for (; pos < max; pos++) {
      ch = state.src.charCodeAt(pos);
      if (ch === 0x5B /* [ */) {
        return false;
      } else if (ch === 0x5D /* ] */) {
        labelEnd = pos;
        break;
      } else if (ch === 0x5C /* \ */) {
        pos++;
      }
    }

    if (labelEnd < 0 || state.src.charCodeAt(labelEnd + 1) !== 0x3A/* : */) {
      return false;
    }

    if (silent) { return true; }

    label = state.src.slice(labelStart, labelEnd).replace(/\\(.)/g, '$1');
    title = state.src.slice(labelEnd + 2, max).trim();
    if (label.length === 0) { return false; }
    if (title.length === 0) { return false; }
    if (!state.env.abbreviations) { state.env.abbreviations = {}; }
    // prepend ':' to avoid conflict with Object.prototype members
    if (typeof state.env.abbreviations[':' + label] === 'undefined') {
      state.env.abbreviations[':' + label] = title;
    }

    state.line = startLine + 1;
    return true;
  }


  function abbr_replace(state) {
    var i, j, l, tokens, token, text, nodes, pos, reg, m, regText, regSimple,
        currentToken,
        blockTokens = state.tokens;

    if (!state.env.abbreviations) { return; }

    regSimple = new RegExp('(?:' +
      Object.keys(state.env.abbreviations).map(function (x) {
        return x.substr(1);
      }).sort(function (a, b) {
        return b.length - a.length;
      }).map(escapeRE).join('|') +
    ')');

    regText = '(^|' + UNICODE_PUNCT_RE + '|' + UNICODE_SPACE_RE +
                    '|[' + OTHER_CHARS.split('').map(escapeRE).join('') + '])'
            + '(' + Object.keys(state.env.abbreviations).map(function (x) {
                      return x.substr(1);
                    }).sort(function (a, b) {
                      return b.length - a.length;
                    }).map(escapeRE).join('|') + ')'
            + '($|' + UNICODE_PUNCT_RE + '|' + UNICODE_SPACE_RE +
                    '|[' + OTHER_CHARS.split('').map(escapeRE).join('') + '])';

    reg = new RegExp(regText, 'g');

    for (j = 0, l = blockTokens.length; j < l; j++) {
      if (blockTokens[j].type !== 'inline') { continue; }
      tokens = blockTokens[j].children;

      // We scan from the end, to keep position when new tags added.
      for (i = tokens.length - 1; i >= 0; i--) {
        currentToken = tokens[i];
        if (currentToken.type !== 'text') { continue; }

        pos = 0;
        text = currentToken.content;
        reg.lastIndex = 0;
        nodes = [];

        // fast regexp run to determine whether there are any abbreviated words
        // in the current token
        if (!regSimple.test(text)) { continue; }

        while ((m = reg.exec(text))) {
          if (m.index > 0 || m[1].length > 0) {
            token         = new state.Token('text', '', 0);
            token.content = text.slice(pos, m.index + m[1].length);
            nodes.push(token);
          }

          token         = new state.Token('abbr_open', 'abbr', 1);
          token.attrs   = [ [ 'title', state.env.abbreviations[':' + m[2]] ] ];
          nodes.push(token);

          token         = new state.Token('text', '', 0);
          token.content = m[2];
          nodes.push(token);

          token         = new state.Token('abbr_close', 'abbr', -1);
          nodes.push(token);

          reg.lastIndex -= m[3].length;
          pos = reg.lastIndex;
        }

        if (!nodes.length) { continue; }

        if (pos < text.length) {
          token         = new state.Token('text', '', 0);
          token.content = text.slice(pos);
          nodes.push(token);
        }

        // replace current node
        blockTokens[j].children = tokens = arrayReplaceAt(tokens, i, nodes);
      }
    }
  }

  md.block.ruler.before('reference', 'abbr_def', abbr_def, { alt: [ 'paragraph', 'reference' ] });

  md.core.ruler.after('linkify', 'abbr_replace', abbr_replace);
};