<!DOCTYPE html> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <bindings xmlns="http://www.mozilla.org/xbl" xmlns:html="http://www.w3.org/1999/xhtml"> <binding id="x"> <content> <html:span class="a"></html:span> <html:span class="b">This should be green</html:span> <children/> </content> </binding> </bindings> <style> #foo { -moz-binding: url("#x"); } .a + .b { color: green; } </style> </head> <body> <span id="foo"></span> </body> </html>