code: function processLine(cm, line, state) {
      var mode = cm.doc.mode;
      var stream = new StringStream(line.text, cm.options.tabSize);
      if (line.text == "" && mode.blankLine) mode.blankLine(state);
      while (!stream.eol() && stream.pos <= cm.options.maxHighlightLength) {
        mode.token(stream, state);
        stream.start = stream.pos;
      }
    }
docs: Lightweight form of highlight -- proceed over this line and update state, but don't save a style array.