When I needed to write a regex character class containing lots and lots of Unicode items, I found that the /x modifier, which allows whitespace and comments in the regex, doesn't help at all within the [...] of a character class. So I needed to find a handy way to break it into multiple lines and even add comments.

I used the trick of interpolating an arbitrary expression using a reference.

my $XML_BaseChar= qr/@{[ "[" . # a character class...
   "\x{0041}-\x{005A}" . # the first range
   "\x{0100}-\x{0131}\x{0134}-\x{013E}\x{0141}-\x{0148}" . # the next 
+range
   "\x{01FA}-\x{0217}\x{0250}-\x{02A8}" . # etc.
   "]"  ]}/;  #here's how to close it up

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Only the stuff inside the quotes appears inside the qr// construct.

In reply to Extend regex legibility within character classes by John M. Dlugosz

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