How do I make one submenu open by default depending on the page...

[wese1991]

So I have a standard two level menu in one php file that I show on all the pages on a website. The menus and submenus are nested <ul> elements. When you go to a page, I would like the submenu that includes that page to be open by default. And also to stay open if another submenu isn't hovered over. I think I can figure out the menu transformations. The part I need help on is finding the submenu that the active page is contained in so I can set that one to be open.