code: function highlightSections (sections, lang) {
    if (!supported(lang)) {
      return sections
    }
  
    // Keep track of the most recent stacks.
    var additionStack
    var deletionStack
  
    sections
      .forEach(function (section) {
        var type = section.type
  
        // Reset the stacks for metadata types.
        if (type === 'header' || type === 'chunk') {
          additionStack = deletionStack = null
  
          return
        }
  
        var value = section.lines.join(SEPARATOR)
        var stack = type === 'deletion' ? deletionStack : additionStack
        var highlight = hljs.highlight(lang, value, false, stack)
  
        // Set the top of each stack, depending on context.
        if (type === 'addition') {
          additionStack = highlight.top
        } else if (type === 'deletion') {
          deletionStack = highlight.top
        } else {
          additionStack = deletionStack = highlight.top
        }
  
        section.lines = highlight.value.split(SEPARATOR)
      })
  
    return sections
  }
docs: Add syntax highlighting to all sections.
  
  @param  {Array}  sections
  @param  {String} lang
  @return {Array}