while(  <DATA>  ) {
        print;

        if(  m/^([a-z_]\w+)=(\d{1,9}|[a-z_]\w*)$/  ) {
            print "($1)($2)\n";
        }

        my( $key, $value );
        ( $key, $value )= m{
            ^
            (
              [a-z_]    # Key name must start with a letter or '_'
              \w        # Subsequent characters can also be digits
              +         # Key names must be at least 2 characters
            )
            =
            (           # The value can be:
              \d        #   If it starts with a digit, it is an integer
              {1,9}     #   Only up to 9-digit values are allowed.
            |           # or, the value can be:
              [a-z_]    #   An identifier must start with a letter or '_'
              \w        #   Subsequent characters can also be digits
              *         #   No length limit on IDs
            )
            $
        }x  &&  do {
            print "# ($1)($2)\n";
            print "# ($key)($value)\n";
        };

        ( $key, $value )= m{
            ^
            (
              [a-z_]    (?# Key name must start with a letter or '_')
              \w        (?# Subsequent characters can also be digits)
              +         (?# Key names must be at least 2 characters)
            )
            =
            (           (?# The value can be:)
              \d        (?#   If it starts with a digit, it is an integer)
              {1,9}     (?#   Only up to 9-digit values are allowed.)
            |           (?# or, the value can be:)
              [a-z_]    (?#   An identifier must start with a letter or '_')
              \w        (?#   Subsequent characters can also be digits)
              *         (?#   No length limit on IDs)
            )
            $
        }x  &&  do {
            print "(?# ($1)($2) )\n";
            print "(?# ($key)($value) )\n";
        };
        print $/;
    }
__END__
this=that
one=12