docs: function (evt) {
                  var stopper = Aria.$window.document.body;
                  var elementId = findByAttribute(evt.target, this.DRAGGABLE_ATTRIBUTE, this.maxDepth, stopper);
                  if (!elementId) {
                      return;
                  }
  
                  var candidate = this._idList.drag[elementId];
                  this.$assert(211, !!candidate);
  
                  this._candidateForDrag = candidate;
                  this._dragStartPosition = {
                      x : evt.clientX,
                      y : evt.clientY
                  };
                  this._dragStarted = false;
  
                  return true;
              }