List of all built-in variables

[Mingun]

I notice that KSC recognises that list of variables in expressions, but not all of them described neigher in User Guide or KSY Reference. Because I implementing alternative compiler I need to known which variables availible and in which contexts.

I found, that KSC has following list of variables (https://github.com/kaitai-io/kaitai_struct_compiler/blob/eb420a617ae91a803659dfc29c8a8b54516b7b70/shared/src/main/scala/io/kaitai/struct/format/Identifier.scala#L77-L86)

• _root
• _parent
• _io
• _
• _buf
• _index
• _on
• _is_le
• _sizeof

Can someone helps me to fill the following table:

Variable	Context	Meaning
_root	instances.<...>.io	Reference to root type in the current file
...	...	...

(Context -- name of KSY property in which expression can be used)

[Mingun]

Once such documentation is created, it will be easier to implement #404