datastore/prop.go
func validPropertyName(name string) bool {
	if name == "" {
		return false
	}
	for _, s := range strings.Split(name, ".") {
		if s == "" {
			return false
		}
		first := true
		for _, c := range s {
			if first {
				first = false
				if c != '_' && !unicode.IsLetter(c) {
					return false
				}
			} else {
				if c != '_' && !unicode.IsLetter(c) && !unicode.IsDigit(c) {
					return false
				}
			}
		}
	}
	return true
}
func validPropertyName(name string) bool {
	if name == "" {
		return false
	}
	for _, s := range strings.Split(name, ".") {
		if s == "" {
			return false
		}
		first := true
		for _, c := range s {
			if first {
				first = false
				if c != '_' && !unicode.IsLetter(c) {
					return false
				}
			} else {
				if c != '_' && !unicode.IsLetter(c) && !unicode.IsDigit(c) {
					return false
				}
			}
		}
	}
	return true
}
// validPropertyName returns whether name consists of one or more valid Go
// identifiers joined by ".".