TTML1 3ED CR2

Hi Nigel et al.,

Per our earlier call, and in anticipation of a potential TTML1 3ED CR2:

- a CR2 branch has been created at https://github.com/w3c/ttml1/pull/357

- PRs for the two outstanding issues (#351 and #354) have been created:

   https://github.com/w3c/ttml1/pull/356
   https://github.com/w3c/ttml1/pull/355

I suggest merging the two PRs and starting a CfC today in case it is
determined that resolving the two issues above must result in a new CR.

Best,

-- Pierre