[mycl]

I think it was in ed already. The POSIX ed spec says: "Any character other than <space> or <newline> can be used instead of a slash to delimit the RE and the replacement."

[codesnik]

and, AFAIR, in perl space and enter could be delimiters too! I think I've used it in some perlgolf task which didn't count whitespace.

[codesnik]

and memory tricked me. Whitespace doesn't work for regex and quoting terminators.

[kbp]

Works in Ruby:

  irb(main):001:1/ puts(%r
  irb(main):002:1* a+
  irb(main):003:0> .match? %q aaa )
  true