code: function() {
              var options = this.getSelected();
  
              // First update the displayed button text.
              if (this.options.enableHTML) {
                  $('.multiselect .multiselect-selected-text', this.$container).html(this.options.buttonText(options, this.$select));
              }
              else {
                  $('.multiselect .multiselect-selected-text', this.$container).text(this.options.buttonText(options, this.$select));
              }
  
              // Now update the title attribute of the button.
              $('.multiselect', this.$container).attr('title', this.options.buttonTitle(options, this.$select));
          }
docs: Update the button text and its title based on the currently selected options.