RegExpr was done to mimic the behavior of regular expressions in Perl 4.0.1.6 for MS-DOS, with a few differences, plus a few additional features introduced in Perl 5.
Consequtive newline characters vbCr and vbLf are treated as two ordinary characters. If you want to match a newline, you must match both vbCr and vbLf, like this:
\s\s
\W\W
\r\f
\n (only if NewLine is set to vbCrLf, that's the default)
Any of these regular expressions will match consequtive vbCr & vbLf.
You can't start or end a range with \n if Const NewLine = vbCrLf (default setting). Use \r and \f instead.
The (?imsx) syntax for setting flags, a feature introduced in Perl 5, is not supported. Flags are set in the function call to RegExpr.
Expressions \L \l \U and \u are not supported, because they are not really part of regular expression matching, but similar to the LCase and UCase functions in VB.