Generally used in a continue block at the end of a
loop to clear variables and reset m?pattern? 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 (m?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.