[WebODF] Foreign elements & cursor positioning

[Philip Peitsch]

Hi everyone,

I have been looking at some funky "valid" ODT documents and discovering some fun
behaviours around cursor positioning. I thought this was a good time to bring up
some potential changes, as I noticed on IRC the other night that Friedrich had also
discovered sometimes the user is unable to place the cursor inside a text:a block.

The existing rules for valid cursor positions only allow placing the cursor
inside what is known as a "grouping element", which is either a span, p or h. This
has already caused me some challenges, because for one of the highlight overlays
I'm doing on top of webodf I need to wrap document text in a normal HTML span,
which then prevents the cursor from entering.

In the situation Friedrich found, there is actually no requirement saying the text
content within a text:a element must be placed in a span.

The suggestion on IRC yesterday was to just add text:a into the grouping element
definitions (a reasonable one), but I got to thinking a little more about whether
this is the best long-term solution. Especially as there are other elements that
could possible contain character data. And for extensibility purposes, ideally
we don't want to have to redo this core cursor positioning logic every time the
UI requires some extra containers and wrappers to help display things :).

Re-reading the ODF specs[1], the preferred approach laid out is actually a
blacklist, not a whitelist as we're currently doing. The blacklist as required
for processing is already defined & used in StyleHelper.isAcceptedNode, is used
for OpRemoveText and OpApplyDirectStyling.

Would anyone have any problems if I changed OdtDocument.TestPositionFilter to use
the blacklist approach instead? The blacklist will need an additional entry to
exclude the cursor as well, so I'll put that in also.

>From my testing with this, it appears to function identically to the existing
approach, with the added bonus of being able to navigate within text:a tags
that don't contain a span :)

Cheers,

Philip

P.S., sorry for all the list spam lately! Apparently I have too much time for
philosophy :)

[1] http://docs.oasis-open.org/office/v1.2/os/OpenDocument-v1.2-os-part1.html#ForeignElementsAndAttributes