That's a freaking dirty programming trick... or undocumented (and
barely supported) implementation detail, depending on how you view
this. It may be usable at the moment, but it may die off with the next
Incidentally, if you look at svy.ado, you see that various commands,
e.g. -ivregress-, get singled out for special treatment. Allowing for
a cmd_svy_check.ado program gives users somewhat similar control with
their own programs.
