function regexp() {
	return /^([-+]?(\d*\.?\d*(?:[eE][-+]?\d+)?|Infinity|NaN)i?)?([-+])?((\d*\.?\d*(?:[eE][-+]?\d+)?|Infinity|NaN)i)?$/;
}
Matches a complex number string.

@private
@returns {RegExp} regular expression

@example
var re = regexp();
// returns /^([-+]?(\d*\.?\d*(?:[eE][-+]?\d+)?|Infinity|NaN)i?)?([-+])?((\d*\.?\d*(?:[eE][-+]?\d+)?|Infinity|NaN)i)?$/