docs: function correctOffset() {
                  var exprOffset = 0;
                  kity.Utils.each(this.expressions, function(expr) {
                      var box = null;
                      if (!expr) {
                          return;
                      }
                      expr.setMatrix(new kity.Matrix(1, 0, 0, 1, 0, 0));
                      box = expr.getFixRenderBox();
                      expr.translate(0 - box.x, exprOffset);
                      exprOffset += box.height + EXPRESSION_INTERVAL;
                  });
                  return this;
              }