code: function updateOptions( $elem, prev, curr ) {
          var bselect = _callMethod( $elem, "element" );
  
          $.each( prev, function(key, val) {
              if ( curr[ key ] !== val ) {
                  if ( key === "size" ) {
                      var sizes = $.map( bootstrapButtonSizes.slice( 0 ), function( size ) {
                          return "bselect-" + size;
                      }).join( " " );
  
                      bselect.removeClass( sizes );
                      if ( bootstrapButtonSizes.indexOf( curr.size ) > -1 ) {
                          bselect.addClass( "bselect-" + curr.size );
                      }
                  }
              }
          });
      }
docs: Updates visual properties of the bselect after the plugin was initialized