code: function getTargetTd(editor, evt) {
  
          var target = domUtils.findParentByTagName(evt.target || evt.srcElement, ["td", "th"], true),
              dir = null;
  
          if( !target ) {
              return null;
          }
  
          dir = getRelation( target, mouseCoords( evt ) );
  
          //如果有前一个节点， 需要做一个修正， 否则可能会得到一个错误的td
  
          if( !target ) {
              return null;
          }
  
          if( dir === 'h1' && target.previousSibling ) {
  
              var position = domUtils.getXY( target),
                  cellWidth = target.offsetWidth;
  
              if( Math.abs( position.x + cellWidth - evt.clientX ) > cellWidth / 3 ) {
                  target = target.previousSibling;
              }
  
          } else if( dir === 'v1' && target.parentNode.previousSibling ) {
  
              var position = domUtils.getXY( target),
                  cellHeight = target.offsetHeight;
  
              if( Math.abs( position.y + cellHeight - evt.clientY ) > cellHeight / 3 ) {
                  target = target.parentNode.previousSibling.firstChild;
              }
  
          }
  
  
          //排除了非td内部以及用于代码高亮部分的td
          return target && !(editor.fireEvent("excludetable", target) === true) ? target : null;
      }
docs: 获取当前拖动的单元格