How the grammar flattens

[Lofton Henderson <lofton@rockynet.com>]

Stuart,

As background our discussion this afternoon, I did this little exercise of 
flattening the EBNF to show what the various options produce (seems worth 
sharing with the TC as well):

** current CGM:1999 grammar with RT/AT/...
** APS proposal using <spanned text> (in RTF file)
** APS proposal using new <partial text substring> production


Currently, if you unwind (flatten) all of the intermediate, non-terminal 
productions in H.3.5, this is what you get for legal RT/AT/.../AT data 
sequences:

<RESTRICTED TEXT> <extent> <point>
<NOT FINAL> <string>
<partial text attribute element>*
<APPEND TEXT> <NOT FINAL> <string>
<partial text attribute element>*
...
<APPEND TEXT> <FINAL> <string>

If we were to change <picture element>* in the <application structure> 
production of H.3.1 to
<picture element>* | <spanned text> , as I originally proposed (current RTF 
file),
then we would get a sequence like this (using some abbreviations) when we 
flatten the EBNF:

<RT> <ext> <pt>
<NOT FINAL> <string>
<partial txt attr elt>*
...
<BEGIN APS>...<BEGIN APS BODY>
<AT> <NOT FINAL> <string>
<partial txt attr elt>*
<END APS>
...
<AT> <FINAL> <string>

It has the somewhat artificial restriction that attributes can only occur 
after the string, at the end of the APS.  Suppose instead we use a new 
production in H.3.1 in the APS body, in place of the current <picture 
element>*:

<picture element>* | <partial text substring>

and define it in H.3.5 with one new production (using some abbreviations 
only for this email convenience):

<partial text substring>  ::=
<partial txt attr elt>*
<AT> <NOT FINAL> <string>
<partial txt attr elt>*

Then when we flatten the EBNF we get results like:

<RT> <ext> <pt>
<NOT FINAL> <string>
<partial txt attr elt>*
...
<BEGIN APS>...<BEGIN APS BODY>
<partial txt attr elt>*
<AT> <NOT FINAL> <string>
<partial txt attr elt>*
<END APS>
...
<AT> <FINAL> <string>

It doesn't really cost much, and removes a rather arbitrary restriction.

Talk to you later,
-Lofton.