Where is full, up-to-date description of T3D files ?

Are there exists good, up-to-date documentation for T3D (Unreal Text File) files? I mean what may the file contain, list of possible properties etc. I can read source files but it will be time-consuming and I would like to avoid it.

I found no really helpful resources.
Legacy:T3D File - Unreal Wiki - only small description
T3D File Format Specification - too old description