@oheil thanks for your response
Now that you’ve explained where it was moved, I found this post which made me think about what might be the Julian way of doing what I wanted.
In my case it was simple enough to re-conceptualize so that the following was suitable:
a isa CustomType
# true
# the above also works for subtypes of CustomType
So my direct issue is solved but I’m kind of annoyed that the documentation, with example, didn’t explicitly mention this (Reflection and introspection · The Julia Language). I feel the info is buried.
But anyway, thanks again.