gpl3 vs. gpl3+

[Alex Kost]

I see that only several packages uses 'gpl3' license.  And I don't
really understand the cases when it should be used instead of 'gpl3+'.

I looked at "aarddict" and "weechat".  They have the same
COPYING/LICENSE files as <http://www.gnu.org/licenses/gpl.txt>.  So it
should be gpl3+, right?

Then I looked at "flexbar".  The only license-related mention in the
source code is "(GPLv3)" in the commentary of "src/Flexbar.cpp":

--8<---------------cut here---------------start------------->8---
   Flexbar - flexible barcode and adapter removal

   Version 2.5  (GPLv3)
--8<---------------cut here---------------end--------------->8---

Is it the case for 'gpl3'?  Are there other cases to use 'gpl3'?

-- 
Alex