It isn't actually anything, ie it's not used as a Perl special variable. However, all punctuation variables are essentially considered special whether they have meaning or not. This is documented in perlvar where it says...
Perl identifiers that begin with digits, control characters, or punctuation characters are exempt from the effects of the package declaration and are always forced to be in package main ; they are also exempt from strict 'vars' errors.
Dave
In reply to Re^3: Missing Bracket
by davido
in thread Missing Bracket
by mkirank
| For: | Use: | ||
| & | & | ||
| < | < | ||
| > | > | ||
| [ | [ | ||
| ] | ] |