Block definitions in partials?

I’m new to Base Templates and Blocks so I’ve been reading about them and tried a few different things to see how they work.

I tried passing a block definition in a partial, but it does not work. I then came across this old thread on GitHub, where bep says that block definitions in partials aren’t supported.

As there have been several new releases since then, I just wanted to check it this is still the case, or perhaps I’m doing something wrong and I’ll share my code for help.