Hi,
Notice that code of `gui--selection-value-internal' and
`org-get-x-clipboard' uses different set of targets and `window-system'
variants. I have no idea if it affects many users. I am in doubts if
there ones running haiku or using SECONDARY selection. However some may
be confused.
Text from PRIMARY and CLIPBOARD selection likely may be obtained from
`gui-selection-value' by fiddling with `select-enable-clipboard' and
`select-enable-primary'. Unfortunately it does not cover SECONDARY
selection and it sounds like boiling a kettle by reducing the problem to
the already solved one <https://www.cl.cam.ac.uk/~hs586/math-jokes.html>
It is just a warning, I am not going to spend more time on this issue.