Generally used in a continue block at the end of a loop to clear
variables and reset ??
 searches so that they work again.  The
expression is interpreted as a list of single characters (hyphens
allowed for ranges).  All variables and arrays beginning with one of
those letters are reset to their pristine state.  If the expression is
omitted, one-match searches (?pattern?
) are reset to match again.  
Only resets variables or searches in the current package.  Always returns
1.  Examples:
Resetting "A-Z"
 is not recommended because you'll wipe out your
@ARGV
 and @INC
 arrays and your %ENV
 hash.  Resets only package
variables; lexical variables are unaffected, but they clean themselves
up on scope exit anyway, so you'll probably want to use them instead.
See my.