Guidelines for parts that are incomplete or undecided

[ehuss]

I think the authoring guide should have some guidelines on when something should be intentionally undecided, and how to state that. (Like certain evaluation orders.)

Some current examples:

• type.pointer.validity.pointer-fragment
• macro.ambiguity.invariant.unseparated-complex-nt

My notes:

• Maybe have something that talks about avoiding accidentally documenting something that is currently undecided.
  • Guidelines on when and how to make notes about parts of the language that are still undecided.