How to interrupt regular expressions?

I am trying to understand regular expressions. I am trying to parse data from XML web service using regular expressions. I need your help to understand few regular expressions.

Regular expressions that I need to understand.

1: https://musicbrainz.org/ws/2/artist/?query=ac%5C%2Fdc //What this 'ac%5C%2Fdc' regular expression in query means?

2: http://musicbrainz.org/ws/2/area/?query=%22%C3%8Ele-de-France%22 //What this '%22%C3%8Ele-de-France%22' regular expression in query means?