static isIdentifierStart(ch) {
		return  (ch >= 65 && ch <= 90) || // A...Z
			(ch >= 97 && ch <= 122) || // a...z
			(ch >= 128 && !Jsep.binary_ops[String.fromCharCode(ch)]) || // any non-ASCII that is not an operator
			(Jsep.additional_identifier_chars.has(String.fromCharCode(ch))); // additional characters
	}
Looks for start of identifier
@param {number} ch
@returns {boolean}