code: function diff (code, lang) {
    var sections = []
  
    code.split(/\r?\n/g).forEach(function (line) {
      var type
  
      if (CHUNK_REGEXP.test(line)) {
        type = 'chunk'
      } else if (HEADER_REGEXP.test(line)) {
        type = 'header'
      } else {
        type = PATCH_TYPES[line[0]] || 'null'
        line = line.replace(/^[+\-! ]/, '')
      }
  
      // Merge data with the previous section where possible.
      var previous = sections[sections.length - 1]
  
      if (!previous || previous.type !== type) {
        sections.push({
          type: type,
          lines: [line]
        })
  
        return
      }
  
      previous.lines.push(line)
    })
  
    return highlightSections(sections, lang)
      .map(function (section) {
        var type = section.type
        var value = section.lines.join(SEPARATOR)
  
        return '<span class="diff-' + type + '">' + value + '</span>'
      })
      .join(SEPARATOR)
  }
docs: Add diff syntax highlighting to code.
  
  @param  {String} code
  @param  {String} lang
  @return {String}