Documentation Fault: droppable activeClass

I'm not sure if I'm the only one, but this example: " $( ".selector" ).droppable( "option", "activeClass", '.ui-state-highlight' );"

does not work for me if I create the class ".ui-state-highlight".

Instead, it works if the command is like this "$( ".selector" ).droppable( "option", "activeClass", 'ui-state-highlight' );", without the "." in the class name declaration.