# No taint implications.
sub A { s/^\s*//; s/\s*$//; return $_; }

# These untaint the return value.
sub B { m/^\s*(.*\S)\s*$/;  return $1; }
sub C { m/(\S+.*\S*)/;      return $1; }
sub D { m/(\S?.*\S*)/;      return $1; }