function invcase( str ) {
	var out;
	var ch;
	var s;
	var i;

	out = [];
	for ( i = 0; i < str.length; i++ ) {
		ch = str[ i ];
		s = uppercase( ch );
		if ( s === ch ) {
			s = lowercase( ch );
		}
		out.push( s );
	}
	return out.join( '' );
}
Converts a string to inverse case.

@param {string} str - string to convert
@returns {string} inverse-cased string

@example
var str = invcase( 'beep' );
// returns 'BEEP'

@example
var str = invcase( 'beep BOOP' );
// returns 'BEEP boop'

@example
var str = invcase( 'isMobile' );
// returns 'ISmOBILE'

@example
var str = invcase( 'HeLlO wOrLd!' );
// returns 'hElLo WoRlD!'