What urls does a page manager intercept? The custom page is set up to intercept /sections/%section.  Will it intercept an URl such as '/section/section-1/articlename' or only '/section/section-1'

Regarding answer from Berdir:
How do I get a custom page to ignore C and respond based upon /A/B regardless of what C value is presented? In my case, C is the name of a specific article of type /A/B and those settings determine the format to be applied to the page through panels. Is there a wildcard?.
It should work the same as hook_menu() implementations and also react when additional path elements are passed to it.

Basically, when you have a request like A/B/C, the menu system first looks for A/B/C, then A/B and finally A until it finds a match.