code: function(_document){
                  var _osc = _document.onselectionchange;
                  if (_osc !== undefined) {
                      try {
                          _document.onselectionchange = 0;
                          return _document.onselectionchange === null;
                      } catch (e) {
                      } finally {
                          _document.onselectionchange = _osc;
                      }
                  }
                  return false;
              }
docs: 是否支持selectionchange
  @param {Object} _document 文档对象