code: function doClick(button) {
  
              inputBox.focus();
  
              if (button.textOp) {
  
                  if (undoManager) {
                      undoManager.setCommandMode();
                  }
  
                  var state = new TextareaState(panels);
  
                  if (!state) {
                      return;
                  }
  
                  var chunks = state.getChunks();
  
                  // Some commands launch a "modal" prompt dialog.  Javascript
                  // can't really make a modal dialog box and the WMD code
                  // will continue to execute while the dialog is displayed.
                  // This prevents the dialog pattern I'm used to and means
                  // I can't do something like this:
                  //
                  // var link = CreateLinkDialog();
                  // makeMarkdownLink(link);
                  // 
                  // Instead of this straightforward method of handling a
                  // dialog I have to pass any code which would execute
                  // after the dialog is dismissed (e.g. link creation)
                  // in a function parameter.
                  //
                  // Yes this is awkward and I think it sucks, but there's
                  // no real workaround.  Only the image and link code
                  // create dialogs and require the function pointers.
                  var fixupInputArea = function () {
  
                      inputBox.focus();
  
                      if (chunks) {
                          state.setChunks(chunks);
                      }
  
                      state.restore();
                      previewManager.refresh();
                  };
  
                  var noCleanup = button.textOp(chunks, fixupInputArea);
  
                  if (!noCleanup) {
                      fixupInputArea();
                  }
  
              }
  
              if (button.execute) {
                  button.execute(undoManager);
              }
          }
docs: Perform the button's action.