Perl Best Practices: Regular Expressions: Always use /xms

• Perl Best Practices - O'Reilly Media

Almost always at least.

DC explains quite well in the beginning of the section on Regular Expressions  [Link], why each of /x, /m, and /s is rather, rather reasonable to use.

• /x : extended formatting / legibility
• /m : let ^ and $ also match next to embedded \n; "multiline mode"
• /s : let . also match newline; "single …"