Amin Bandali <bandali@gnu.org> wrote:
> Ludovic Courtès <ludo@gnu.org> writes:
>> I would propose GFDLv1.3+ without invariant sections, since that can then be relicensed to CC-BY-SA should anyone need it.
>
> but reading the text for GFDLv1.3, specifically "11. RELICENSING", it seems to me that the explicit permission to relicense GFDLv1.3-covered work to CC BY-SA 3.0 was only valid until August 1, 2009.

And it had been never valid for any blog, only for a ‘wiki’.

> I would suggest explicitly asking the FSF or seeking legal advice about that, to know whether that section still applies today.

If one finds the licence itself unclear, there is also a FAQ [1].

[1] https://www.gnu.org/licenses/fdl-1.3-faq.html

> Another good candidate is CC BY-SA 4.0, which was declared one-way compatible with GPLv3...

...yet not with FDL (which Guix manual is under).

> I have also seen folks license material on their site under GPLv3+.

And neither licence is mutually exclusive with the other one!