There are four aspects of Private Use Area characters which I would like to mention in relation to your project.
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As your script is not regular Unicode, it would, in my opinion, be best to implement your script (as such) in the Private Use Area.
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With a script such as Devanagari which is regular Unicode, there is also the possibility of using the Private Use Area, namely for the ligatures.
This is not to exchange them over communications systems but so that someone wishing, say, to produce a graphic for a web page or to print out a page using an application such as Microsoft WordPad, yet not having an OpenType font and advanced software to use it, can still get a display as desired, although with manual ligature entry.
For example, the Code2000 font, which is available as shareware on the web, has ligatures for Tamil in the Private Use Area.
So, I am suggesting that you would have two sets of glyphs in the Private Use Area, one for the script itself, just because it is not regular Unicode, and another for the ligatures, those ligatures being in the Private Use Area regardless of whether they are for a script which is itself in regular Unicode or in the Private Use Area. You might like to consider separating them, like perhaps putting the script starting at U+E400 and the ligatures starting at U+EF00. Those places are not arbitrary, I have suggested that ligatures for actual Indian scripts are encoded starting at U+EC00 for use in digital broadcasting using the MHP system. http://www.mhp.org So, placing the ligatures for your script at U+EF00 fits in with that.
(As an aside, the idea is not to broadcast the code points for the ligatures, they are mapped because the font technology used, Portable Font Resource, appears to have no glyph substitution facilities, so they need to be mapped somewhere if they are to be available in a font. The substitution would be done in the television set by a Java program which is broadcast.)
- If you want to try a font which has characters in the Private Use Area, then my Quest text font may be useful.
http://www.users.globalnet.co.uk/~ngo/fonts.htm
For example, try entering U+E707 which is decimal 59143 and which is a ct ligature for fancy English printing. I did a list of code points for such ligatures in 2002.
http://www.users.globalnet.co.uk/~ngo/golden.htm
- In order to insert Private Use Area characters into a font one may use Insert | Glyphs in Font Creator 5.0. Then, for each in turn, highlight the rectangle, right click and use Properties to map using the Microsoft platform. Enter something such as U+EF01 as $EF01 then click Add and then click OK. After adding them, however many you want, use Format | Post to generate the postscript names. For this example, it would be uniEF01 not anything specific to the particular application of the Private Use Area codes.
I hope that this helps.
William Overington