code: function appendDecorations(basePos, sourceCode, langHandler, out) {
      if (!sourceCode) { return; }
      var job = {
        sourceCode: sourceCode,
        basePos: basePos
      };
      langHandler(job);
      out.push.apply(out, job.decorations);
    }
docs: Apply the given language handler to sourceCode and add the resulting
  decorations to out.
  @param {number} basePos the index of sourceCode within the chunk of source
  whose decorations are already present on out.