code: function isSupportedElement( element, mode ) {
  		if ( mode == CKEDITOR.ELEMENT_MODE_INLINE )
  			return element.is( CKEDITOR.dtd.$editable ) || element.is( 'textarea' );
  		else if ( mode == CKEDITOR.ELEMENT_MODE_REPLACE )
  			return !element.is( CKEDITOR.dtd.$nonBodyContent );
  		return 1;
  	}
docs: Asserting element DTD depending on mode.