This feature is only available in Inspector Gadgets Pro.
These attributes can be placed on properties in shaders to modify their appearance and behaviour in the Inspector much like Decorator Attributes do in regular scripts. Unity comes with several of these attributes listed in the Unity Manual (look under the Property attributes and drawers headding).
Currently Inspector Gadgets only has one of these attributes, so if you have any suggestions for new ones please email firstname.lastname@example.org.
[TexDefine] attribute can be placed on texture properties to specify a keyword that will be added to the material whenever a texture is assigned to the property. This allows you to more easily create Shader Variants.