selector args to plural/collection methods

[jarib]

browser.divs(:class => "foo") #=> DivCollection

[jarib]

As part of the window switching stuff, I've changed so that a selector argument is allowed and passed to the ElementCollection constructor. So what remains is actually filtering the elements.

It looks like this is mostly implemented in ElementLocator - at the end of #find_by_conditions we do actually find all matching elements when :index is passed by calling #elements_by_idents. The ElementLocator class badly needs refactoring though.