code: func lexNumber(l *lexer) stateFn {
  	typ, ok := scanNumber(l)
  	if !ok {
  		return l.errorf("bad number syntax: %q", l.input[l.start:l.pos])
  	}
  	// Emits itemFloat or itemInteger.
  	l.emit(typ)
  	return lexInsideTag
  }
docs: // lexNumber scans a number: a float or integer (which can be decimal or hex).