code: function convertStyleToRules( style ) {
  		var styleDef = style.getDefinition(),
  			rules = {},
  			rule,
  			attrs = styleDef.attributes;
  
  		rules[ styleDef.element ] = rule = {
  			styles: styleDef.styles,
  			requiredStyles: styleDef.styles && CKEDITOR.tools.objectKeys( styleDef.styles )
  		};
  
  		if ( attrs ) {
  			attrs = copy( attrs );
  			rule.classes = attrs[ 'class' ] ? attrs[ 'class' ].split( /\s+/ ) : null;
  			rule.requiredClasses = rule.classes;
  			delete attrs[ 'class' ];
  			rule.attributes = attrs;
  			rule.requiredAttributes = attrs && CKEDITOR.tools.objectKeys( attrs );
  		}
  
  		return rules;
  	}
docs: Convert CKEDITOR.style to filter's rule.