Shortest unmatchable regular expression Your mission is to write the shortest valid regular expression that no string can match, empty string included.

Submissions must have this form ("literal notation"):

/pattern/optional-flags


Shortest regexp wins. The regexp size is counted in characters. (including slashes and flags)

Please explain how your regexp works (if it's not trivial)

Thanks, and have fun!
6 chars

Following on the answers of primo and Peter Taylor, and a hint from man perlre:

/(?!)/

This perl-compatible regex matches an empty string which is not followed by another empty string.