Sets a custom attribute value for a given glyph.
- macOS 10.3+
The custom attribute.
The new attribute value.
Index of the glyph whose attribute is set.
Custom attributes are glyph attributes such as
NSGlyph or attributes defined by subclasses. Subclasses that define their own custom attributes must override this method and provide their own storage for the attribute values. Nonnegative tags are reserved; you can define your own attributes with negative tags and set values using this method.