promql/lex.go
func lexIdentifier(l *lexer) stateFn {
	for isAlphaNumeric(l.next()) {
		// absorb
	}
	l.backup()
	l.emit(ItemIdentifier)
	return lexStatements
}
func lexIdentifier(l *lexer) stateFn {
	for isAlphaNumeric(l.next()) {
		// absorb
	}
	l.backup()
	l.emit(ItemIdentifier)
	return lexStatements
}
// lexIdentifier scans an alphanumeric identifier. The next character
// is known to be a letter.