For me, focus goes to the next input, which seems correct. That is:

• If I press tab, the selection is confirmed and focus moves to the next input.
• If I press return, the selection is confirmed but focus does not move.

The intent is that tab means "done with all selections; move to the next input" and return means "done with this selection".

This behavior seems consistent across forms.

Are you seeing a different behavior, or do you not think this behavior is reasonable? It seems reasonable/desirable to me.

Oh! I didn't think of hitting enter (I'm used to tab-completing instead).

Enter works great.

The intent is that tab means "done with all selections; move to the next input" and return means "done with this selection".

In, say, gmail, if you're composing a new email and you start typing in the 'to' field, suggestions will pop up, and if you want to take the selection you hit 'tab', at which point it autocompletes and puts the cursor next to the token to wait for the next name to be input -- the same as how enter works for phabricator. I just tested now and enter works the same as tab for gmail.

Personally, I prefer the gmail semantics. The current phabricator semantics are a bit confused, I think, because while in completion mode -- that is, while phabricator is suggesting auto-completes -- tab both finishes the autocomplete and moves to the next input: it seems like tab is being passed through to both the autocomplete logic and to the element logic. To me, it makes more sense that while autocompleting, all inputs are passed just to the autocomplete logic, and in that logic both tab and enter mean "accept this autocomplete".

That said, I have a happy workaround now that I know to use enter. I do still think changing the tab behavior while autocorrecting would be reasonable. An alternative would be to make the enter behavior easier to discover, though I don't know a reasonable way to do that.

I don't think expecting people to hit enter is entirely reasonable – I'm personally scared that it'll submit the form, which is what enter ordinarily does in a form (except in a textarea).

tab and enter both seem correct / commonly used in this UEX, at least from my limited testing of a few mail clients, gmail, facebook, etc.