tl;dr
Found a workaround. Raku documentation about meta / config data is
subtly wrong. I'm writing a PR to modify documentation.
Long version:
As per my previous email, the documentation in docs.raku.org about POD6
says that configuration data provided on lines after a POD6 declaration
has not been implemented.
This is wrong in some way, either the implementation is incorrect, or
the documentation is incorrect. But config data CAN be supplied on
succeeding lines.
What does not work (in that 'newkey' is not found in the 'config' part
of the Pod::Block returned by $=pod
=head1 :key<value>
= :newkey<newvalue>
But this does work, and it is a passing test in the Roast suite
=head1 :key<value>
= :newkey<newvalue>
However, the intent of S26, as stated in the raku documentation, is for
the first variant above to work, and also for the following case
(this being what is intended as a virtual margin):
=head1 :newkey<value>
= :newkey<newvalue>
But this does works (and it seems to be two virtual margins)
=head1 :key<value>
= :newkey<newvalue>
I have looked at the grammar for this situation, which I think is at
https://github.com/finanalyst/rakudo/blob/ae2bf80dae74986c75f9a610f7a25cc1f6cdbb36/src/Perl6/Grammar.nqp#L5093
but I cannot see why the actual behaviour occurs, but the documented
(apparently intended) behaviour does not.