I second placeholder as the most rational keyword. Every description of the
distinct usage of type alias refers to is a placeholder type. placeholder is
one word(circumventingCase_issues) and is more descriptive of what it is than
associated*. Seems like an easy win. Is there a some reason I am
Summary of feedback
Cons
Block based API prevents return/break/continue
Can be implemented by an extension without language changes
Vaguely confusable with multiplication
Pros
Is easier for new learners
Removes ambiguity of ..< vs ... (again mostly new learners)
shorter than existing syntax
