Is ${x+word} documented?

[Peng Yu]

Hi,

I don't find the usage of `${x+word}` documented in the manpage (in
the Parameter Expansion section). Do I miss something here?

Can I always assume ${x:+word} and ${x+word} are exactly the same?

$ x=1
$ echo ${x:+word}
word
$ echo ${x+word}
word

-- 
Regards,
Peng