Hi Henrique,

> would anyone out there happen to know how did arabic DOS, on the old 
> days, deal with:
> 1) The control characters needed to handle the script - ZWJ (Zero-width 
> joiner), ZWNJ (zero-width non-joiner), RLM (right-to-left mark), LRM 
> (left-to-right mark) and control characters needed to handle bilingual 
> text (LTR and RTL) in a same sentence: RLE/LRE (right-to-left and 
> left-to-right embedding), RLO/LRO (right-to-left and left-to-right 
> override) and PDF (POP directional Formatting).

All of those sound like control characters which would have
to be understood by DISPLAY or similar and which will need
space in the codepage, possibly in lesser used control char
areas (ASCII 0 to 31 somewhere). Without having to have any
specific shape, so in a character table, 0 to 31 ASCII will
still look like ASCII but you would not be able to "print"
those any more, at least without using escape sequences...?

> 2) Codepage 720 and many others which only present the isolated shapes 
> of the characters. DOS, seemingly, had somehow to rely on subfonts or 
> any feature which would cause DOS to trade the characters' isolated 
> shapes for their initial, medial or final shapes on-the-fly as the text 
> was typed.

Maybe it just looked ugly and used non-contextual shapes? ;-)

> 3) Combining chars. All arabic codepages, including cp864, include at 
> least two codepoints which present them.

You mean Unicode would represent them either as pre-combined
or as some character plus a separate accent "character"? Not
something that DOS is likely to have cared about, probably
it only used pre-composed characters and had the characters
without accent as separate entities, just like Latin vowels
and Latin accented vowels (umlauts etc) having separate full
shape font items in CP850 and similar. Note that CP850 does
not even have "double dot above" for composition, it only
has that as part of pre-composed umlaut character stapes...

> Hebrew DOS is a simpler case yet topic #3 also applies to the script 
> and, with the exception of control characters ZWJ and ZWNJ, topic #1 
> also does.

So it is interesting to hear how Hebrew codepages "tick" :-)


AppSumo Presents a FREE Video for the SourceForge Community by Eric 
Ries, the creator of the Lean Startup Methodology on "Lean Startup 
Secrets Revealed." This video shows you how to validate your ideas, 
optimize your ideas and identify your business strategy.
Freedos-user mailing list

Reply via email to