Found this thread when I was looking for a quicker route to the Advanced Selector than right clicking. I thought the ctrl+middle button sounded great - but it doesn't quite work how I'd expected. I wanted to use it to select faces when adding constraints, but triggering the Advanced Selector by that method seems to be limited to selecting entire components? Whereas right clicking and picking it from the menu allow selection of faces.
Bug, or feature?
UPDATE not sure where this is documented, but I missed it... when applying constraints, the middle button alone (without ctrl) activates the advanced selector window.