Teletext control codes

[William_J_G Overington]

In the document

Proposal to add further characters from legacy computers and teletext to 
the UCS

https://www.unicode.org/L2/L2021/21235-terminals-supplement.pdf

at the end ogf page 4 is the following.

> Control characters from microcomputer platforms and teletext were also 
> determined to be out of scope for the UCS. These characters were 
> located in what would today be considered the C0 control range 
> (0x00–0x1F) or the C1 control range (0x7F–0x9F). Processes that need 
> to interchange these codes should simply interchange the binary C0 or 
> C1 value, extended to the UCS code space but without further mapping. 
> Emulators should treat these control codes as appropriate for the 
> targeted environment.

In relation to teletext control codes, my opinion is that they need to 
be encoded separately from the C0 control range. This would ensure that 
in interchange that none of the teletext control codes is ever 
misinterpreted as having the basic C0 character meaning.

There was no ambiguity possible in a teletext system.

In a viewdata system where the display was almost similar, there would 
have been ambiguity and so the control characters for viewdata systems 
were encoded not in the C0 set so as to avoid clashing between the 
teletext character set as used for viewdata and and the basic control 
characters. I remember that the signaling system used for control 
characters in viewdata was explained in an article by Mr S Fedida in an 
issue of Wireless World, before September 1977.

It may have been one article in a four article sequence, spread over 
four issues of the magazine.

https://en.wikipedia.org/wiki/Samuel_Fedida

One possibility is to encode the teletext control characters as a block 
of 32 code points in plane 14, without closing up the unused points. 
These characters in plane 14 would be displayable characters and thus 
not control characters in non-teletext-emulating systems, each displayed 
as a glyph specified in The Unicode Standard as two small capital 
letters arranged one above the other, but not overlapping. For example A 
above G for Alphanumerics Green.

I opine that it would be good for the proposal be extended to include 
encoding of the teletext control characters please.

Could we discuss this please?

William Overington

Thursday 16 December 2021