More Detail for Variable Declarations

[librasteve]

New feature

New feature request in doc content...

Include the clarifications on declarations and scope set out here:

https://stackoverflow.com/a/66056086/9146565

to go somewhere near this existing content:

https://docs.raku.org/language/variables#Variable_declarators_and_scope

[arkiuat]

I've started working on this. @jnthn's discussion mostly ranges over lexical vs package scope, my vs our, so I'm trying to condense this down to two neat sections that can be added respectively to the my and our subsections of the location @librasteve suggests above.