> I don't understand: you first seem to say you disagree with me, but then
 > what you say afterwards seems to agree with me.

Indeed.

 > Indeed, but otherwise, as you pointed out, it makes the semantics rather
 > tricky if window-persistent-parameters is changed between the save and
 > the restore (which is something that is very likely to happen sometimes
 > since the restore may happen years after the save).

I resolved the semantics by saving always all parameters unless I do
`window-state-get' with IGNORE non-nil and the parameter is in
`window-state-ignored-parameters'.  When restoring parameters via
`set-window-configuration'/`window-state-put', I overwrite/install a
value only if the parameter is in `window-persistent-parameters'.

martin