text: // Utility function that allows modes to be combined. The mode given
  // as the base argument takes care of most of the normal mode
  // functionality, but a second (typically simple) mode is used, which
  // can override the style of text. Both modes get to parse all of the
  // text, but when both assign a non-null style to a piece of code, the
  // overlay wins, unless the combine argument was true, in which case
  // the styles are combined.
  
  CodeMirror.overlayParser = function(base, overlay, combine) {
    return {
      startState: function() {
        return {
          base: CodeMirror.startState(base),
          overlay: CodeMirror.startState(overlay),
          basePos: 0, baseCur: null,
          overlayPos: 0, overlayCur: null
        };
      },
      copyState: function(state) {
        return {
          base: CodeMirror.copyState(base, state.base),
          overlay: CodeMirror.copyState(overlay, state.overlay),
          basePos: state.basePos, baseCur: null,
          overlayPos: state.overlayPos, overlayCur: null
        };
      },
  
      token: function(stream, state) {
        if (stream.start == state.basePos) {
          state.baseCur = base.token(stream, state.base);
          state.basePos = stream.pos;
        }
        if (stream.start == state.overlayPos) {
          stream.pos = stream.start;
          state.overlayCur = overlay.token(stream, state.overlay);
          state.overlayPos = stream.pos;
        }
        stream.pos = Math.min(state.basePos, state.overlayPos);
        if (stream.eol()) state.basePos = state.overlayPos = 0;
  
        if (state.overlayCur == null) return state.baseCur;
        if (state.baseCur != null && combine) return state.baseCur + " " + state.overlayCur;
        else return state.overlayCur;
      },
      
      indent: function(state, textAfter) {
        return base.indent(state.base, textAfter);
      },
      electricChars: base.electricChars
    };
  };