If I have a list of books' call numbers in Dewey Decimal in a buffer, is this something I could sort with Emacs regex -- or is this an elisp task? For example, 261.1 C87 comes before 261.104 Z99 because the first one can be understood as 261.100 C87. So each column/place must be compared. And then of course the alphabet parts, which means 261.1 C87 comes before 261.1 Ch2. I'm just wondering if there are any Emacs regex experts who would see a good way. Otherwise, I'll just do elisp on it.