TT and subtitling/captioning - separating timing from style from content - temporal flow of content

Dear TT-WG,

For those that don't know me -  I am a software engineer for a company that
produces subtitling (captioning) equipment 
- so all my comments should be taken in that context.

I have just been reading through the F2F minutes for March on the TT-WG home
page, 
and have two questions regarding the tentative model that seems to be
appearing for TT-AF.

Assuming that I wish to separate the timing in my TT-AF document from the
content 
- by using references within the timing 'tree' a la Daisy model - and
assuming that this might be possible! 
- would it then possible to apply style through the timing tree rather than
by inline markup or attribute within the text content.

I.e. - using example (crudely hatcheted from GA examples)

<seq>
<ref id="T27" dur="3s"/>
<ref id="T28" begin="T27.end " dur="3s"/>
</seq>

<tt:content id="T27">
 Some text with some&nl; Hard line breaks.
</tt:content>

<tt:content id="T28">
 Some more text with some&nl; Hard line breaks.
</tt:content>

will it be possible to do something like this.... (in spirit if not in
exactly this manner...)?

<seq>
<ref id="T27" dur="3s" style="text-indent:10pt"/>
<ref id="T28" begin="T27.end " dur="3s" style="font-size:14pt"/>
</seq>

<tt:content id="T27">
 Some text with some&nl; Hard line breaks.
</tt:content>

<tt:content id="T28">
 Some more text with no Hard line breaks.
</tt:content>

further - might it be possible to replace the style attribute above 
with a reference to an element (or portion of a style sheet)
that defines the style (to avoid multiple large style attribute
definitions)? E.g.

<seq>
<ref id="T27" dur="3s" style="S1"/>
<ref id="T28" begin="T27.end " dur="3s" style="S2"/>
</seq>

<tt:content id="T27">
 Some text with some&nl; Hard line breaks.
</tt:content>

<tt:content id="T28">
 Some more text with no Hard line breaks.
</tt:content>

<StyleDef id="S1" defn="text-indent:10pt"/>
<StyleDef id="S2" defn="font-size:14pt"/>


A second question....

It would be desirable for TT (at least IMHO) to include mechanisms for
describing the temporal breaking of content. 
What I am thinking of is a document that does not describe explicitly the
timing for all of the content 
- but rather describes that X amount of content fits into a box of size Y
over a time period of Z. 
Now if the content X is too large for box Y - how does the content get
over(?)flowed in a 'temporal sense' through the box. 
This is a 'crux' issue in subtitling / captioning.

regards 
John Birch

The views and opinions expressed are the author's own and do not necessarily
reflect the views and opinions of Screen Subtitling Systems Limited.