this keyword shouldn't exist outside of a struct

[d0c-s4vage]

The this keyword as strictly defined by 010 editor is (docs):

The this keyword can be used to access the variable representing the current structure being defined

and

If no current structure is currently being defined, this is NULL.

Pfp has a slightly different approach, where all top-level fields are part of an implicit struct, which makes this never equal to NULL.