In this case `ret` is a table not containing the node, which makes
pubsub_error_reply() try to get an error template with that `ret` table
as index, which returns a `nil` then passed to table.unpack, which in
turn throws the error.
Clients would generally be using the "max" symbol instead of discovering
this, but this also gets us validation and earlier rejection of out of
bounds values.
Default left as 'never' in mod_pubsub to preserve the previous behavior.
Unclear if this is desirable, but can always be changed later.
In mod_pep this allows turning off the automatic resending of most
recent item.
Examples in XEP-0060 suggest that items should be listed in
chronological order, but we get them from the archive in reverse
order.
However when requesting specific items by id the results keep that
order and we don't want to flip it again.
At some point it would likely be best to use the archive API directly
instead of this util.cache-compatible wrapper.
This would also release any resources held via references from these
callbacks.
I'm not sure why we don't just re-new() the whole thing.
Related to #1382
Because of the way the previous pubsub service is carried access module
reloads, it would retain the configuration options with their previous
values from when the service was first created.
XEP-0060 says that this the way to indicate that 'persistent-items' is
unsupported, but doesn't explicitly say if it being disabled in the node
configuration also counts as unsupported.
Since nodes were always persistent according to the XEP-0060 definition.
Whether data is stored in memory or on disk was not what this setting
was meant for.
All the XEP-0060 examples have the publisher attribute set to a bare
JID, but the text does allow it to be the full JID.
Since mod_pubsub is more likely used for open nodes that anyone can
subscribe to it makes sense to not leak the full JIDs. This is also
disabled by defaults.
In mod_pep on the other hand it might make sense to have the full JID
since that data is more likely to be broadcast to contacts which are
already somewhat trusted.
XEP-0060 6.2.2
This is a MAY but it makes it nice and symmetric with the subscription
response. Reduces the need to remember which node you unsubscribed from.
Explicit > implicit etc.
in order to avoid conflict with a handler at the default (0) priority,
making it easier to write your own formatting in plugins.
this follows the common pattern of default modules having lower priority
This most likely was copied from the handling of <retract/>, where it actually
is required by the spec (XEP-0060 §7.2.2.1), but this attribute doesn’t exist
for purge.
