Type of a shader keyword, eg: built-in or user defined.
See Also: ShaderKeyword.
| None | No type is assigned. |
| BuiltinDefault | The keyword is built-in the runtime and it is systematically reserved. |
| BuiltinExtra | The keyword is built-in the runtime and it is optionally reserved depending on the features used. |
| BuiltinAutoStripped | The keyword is built-in the runtime and can be automatically stripped if unusued. |
| UserDefined | The keyword is defined by the user. |