completion in between non-spaces

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Having solved completion after a non-space, but on a space, we need to
raise the bar and repeat the following everyday feat in bash:

tar cvf /home/user/dir/something

<== now you want to change dir to dirmore, left-arrow over / after
dir, and hit tab -- if there's a clear dirmore completion prefix, bash
will fill it in with no spaces.  But zsh refuses and I need to open up
a space and close it later.

Is it doable in teh midst of chars?

Cheers,
Alexy