Hello, [this is my first post here]
Unless I missed someting, there is an error in
http://calibre-ebook.com/user_manual/regexp.html
After introducing character classes and wildcards, there is a "Note" in the "Hey Neat, this is starting to make sense" section. The note refers to the ".", which has not yet been introduced. In fact, after that the dot is regularly used.
Apparently in some edit, the introduction to the dot got removed. For first-timers this could be very very confusing.