callsite.md

1. ref and ref readonly parameters require the arguments are an lvalue and ...

   1. Use ref as a call site annotation for either
   2. Use in as a call site for ref readonly
   3. Using no annotation is allowed for ref readonly but leads to a warning, for ref it leads to an error
   4. Using out at the call site leads to an error

2. in parameters require the arguments ...

   1. Use in or no annotation at the call site
   2. Using ref at the call site is allowed but leads to a warning
   3. Using out at the call site leads to an error

Other Items:

• ref readonly will not be allowed on operators