Make contributory properties unavailable except internal use

This change follows [UAX #44 5.13 Property APIs].

> The following subtypes of Unicode character properties should generally not be exposed in APIs,
> except in limited circumstances. They may not be useful, particularly in public API collections,
> and may instead prove misleading to the users of such API collections.
>
>   * Contributory properties are not recommended for public APIs.
> ...
https://unicode.org/reports/tr44/#Property_APIs

1 files changed, 13 insertions, 0 deletions

diff --git a/ucd/api.go b/ucd/api.go
index 6451f39..0212e01 100644
--- a/ucd/api.go
+++ b/ucd/api.go
@@ -39,6 +39,19 @@ func NormalizeCharacterProperty(propName, propVal string) (string, error) {
 	return b.String(), nil
 }
 
+func IsContributoryProperty(propName string) bool {
+	if propName == "" {
+		return false
+	}
+	
+	for _, p := range contributoryProperties {
+		if propName == p {
+			return true
+		}
+	}
+	return false
+}
+
 func FindCodePointRanges(propName, propVal string) ([]*CodePointRange, bool, error) {
 	if propName == "" {
 		propName = "gc"