gistfile1.txt

			var editor = CKEDITOR.replace( 'editor1', {
				plugins: 'wysiwygarea'
			} );

			editor.on( 'instanceReady', function() {
				editor.addCommand( 'foo', {
					allowedContent: new CKEDITOR.style( {
						element: 'a',
						attributes: {
							'!href': '',
							'target': ''
						}
					} ),
					requiredContent: new CKEDITOR.style( {
						element: 'a',
						attributes: {
							href: ''
						}
					} )
				} );

				editor.addFeature( editor.getCommand( 'foo' ) );
			} );