Designing a format for research use of the PUA in a RTL mode (from Re: RTL PUA?)

On Monday 22 August 2011, William_J_G Overington <wjgo_10009_at_btinternet.com> wrote:
 
> Would a third option work?
> 
> In the Description section of the Macintosh Roman section of a TrueType font, include a line of text in a plain text format of which the following line of text is an example.
> 
> PUA.RTL="$E000-$E1FF,$E440-$E447,$E541,$E549,$E57C,$EA00-$EA0F,$EC07";
> 
> One could specify precisely which Private Use Area characters were to become RTL when using that particular font.
> 
> One would need rendering software that looked for such a string of text in the font file, yet, as far as I am aware, no approval from any committee in order to put this solution into practical use.
 
Thinking further on this, I am putting forward the following suggestion for discussion, in the hope that it might be of use.
 
Suppose that a  a "special researcher's edition" of a wordprocessing application or a desktop publishing application at start up looks in a specified directory for a file with the following file name.
 
pua_major.txt
 
If pua_major.txt exists, then it is opened and it is searched for a PUA.RTL assignment statement. If a PUA.RTL assignment statement is not found in the file, it is taken as if the following had been included in the file.
 
PUA.RTL="";
 
If pua_major.txt is found, then that is an end of the searching process and no search for PUA.RTL would take place in a font file.
 
If pua_major.txt is not found, then the application looks in a specified directory for a file with the following file name.
 
pua_minor.txt
 
If pua_minor.txt exists, then it is opened and it is searched for a PUA.RTL assignment statement. If a PUA.RTL assignment statement is not found in the file, it is taken as if the following had been included in the file.
 
PUA.RTL="";
 
Also, if the file is not found, the PUA.RTL assignment statement is taken as the following.
 
PUA.RTL="";
 
However, the value of PUA.RTL thus determined would be kept in reserve and only used if there were no PUA.RTL assignment statement in the font that is being used.
 
This method would allow the choice of where to specify right-to-left directionality for some Private Use characters to be made either as being in a font file or in a text file, with the choice of whether the text file is an override or a backup of any such information within a font.
 
Would such a format solve the needs of those who want to use right-to-left Private Use characters? If not, could people say what other features are needed please in the hope that a suitable system can be specified by consensus within this thread?
 
William Overington
 
23 August 2011
Received on Tue Aug 23 2011 - 08:01:02 CDT