- tag arrays. Each array is terminated by 0. If the first
- element is 0xFFFFFFFF, apply all the features except those that
- appear in the following elements. It may be NULL if there are
- no features. */
+ tag arrays. Each array is terminated by 0. It may be NULL if
+ there is no feature to specify.
+
+ (1) The case of using this information for selecting which
+ features to apply to a glyph string. If the array is NULL,
+ apply no feature. If the first element is 0xFFFFFFFF, apply all
+ available features except for what appear in the second and
+ following elements (if any). Otherwise, apply all listed
+ features.
+
+ (2) The case of using this information for checking if a a font
+ can be drived by a specific FLT. If the array is NULL, the font
+ should not have any features. Otherwize, the font should have
+ all features before 0xFFFFFFFF element (if any) and should not
+ have any features after that element. */