code: function setMceInternalContent(e) {
          var selectionHtml, internalContent;
  
          if (e.dataTransfer) {
            if (editor.selection.isCollapsed() && e.target.tagName == 'IMG') {
              selection.select(e.target);
            }
  
            selectionHtml = editor.selection.getContent();
  
            // Safari/IE doesn't support custom dataTransfer items so we can only use URL and Text
            if (selectionHtml.length > 0) {
              internalContent = mceInternalUrlPrefix + escape(editor.id) + ',' + escape(selectionHtml);
              e.dataTransfer.setData(mceInternalDataType, internalContent);
            }
          }
        }
docs: Sets Text/URL data on the event's dataTransfer object to a special data:text/mce-internal url.
  This is to workaround the inability to set custom contentType on IE and Safari.
  The editor's selected content is encoded into this url so drag and drop between editors will work.
  
  @private
  @param {DragEvent} e Event object