code: function( filter ) {
  			if ( !filter )
  				filter = this.filter;
  
  			if ( this.activeFilter !== filter ) {
  				this.activeFilter = filter;
  				this.fire( 'activeFilterChange' );
  
  				// Reseted active filter to the main one - reset enter modes too.
  				if ( filter === this.filter )
  					this.setActiveEnterMode( null, null );
  				else
  					this.setActiveEnterMode(
  						filter.getAllowedEnterMode( this.enterMode ),
  						filter.getAllowedEnterMode( this.shiftEnterMode, true )
  					);
  			}
  		}
docs: Sets the active filter ({@link #activeFilter}). Fires {@link #activeFilterChange} event.
  
  // Set active filter which allows only 4 elements.
  // Buttons like Bold, Italic will be disabled.
  var filter = new CKEDITOR.filter( 'p strong em br' );
  editor.setActiveFilter( filter );
  
  Setting new filter will also change the {@link #setActiveEnterMode active enter modes} to the first values
  allowed by the new filter (see {@link CKEDITOR.filter#getAllowedEnterMode}).
  
  @since 4.3
  @param {CKEDITOR.filter} filter Filter instance or a falsy value (e.g. `null`) to reset to the default one.