diff style regexps?

[jidanni]

In (info "(diff)Comparing Directories"):
  Unlike in the shell, a period at the start of the base of a file name
  matches a wildcard at the start of a pattern.

OK, but in my brain there are
1. shell glob REGEXPs
2. perl/egrep/sed REGEXPs (perl needs less backslashes that the other two)
Are you saying you have now invented a third hybrid? Please clarify
the sentence.
It seems you are hinting that you are using perl REGEXPs when maybe
you only mean for character 1.
Better say explicitly what . will do in other positions, else that's
what we think you are hinting.