function callbackBody( ch1 ) {
	if ( isComplexChar( ch1 ) ) {
		return '// ...';
	}
	if ( ch1 === 'x' ) {
		return 'return true;';
	}
	if ( ch1 === 'd' ) {
		return 'return 3.0;';
	}
	if ( ch1 === 'f' ) {
		return 'return 3.0f;';
	}
	return 'return 3;';
}
Returns a callback body based on the callback output data type.

@private
@param {string} ch1 - one-letter character abbreviation for output value
@returns {string} callback body