IDC's versus Egyptian format controls (was: Re: Why so much emoji nonsense?)

[Ken Whistler via Unicode]

On 2/16/2018 8:00 AM, Richard Wordingham via Unicode wrote:

> A more portable solution for ideographs is to render an Ideographic
> Description Sequences (IDS) as approximations to the characters they
> describe.  The Unicode Standard carefully does not prohibit so doing,
> and a similar scheme is being developed for blocks of Egyptian
> Hieroglyphs, and has been proposed for Mayan as well.

A point of clarification: The IDC's (ideographic description characters) 
are explicitly *not* format controls. They are visible graphic symbols 
that sit visibly in text. There is a specified syntax for stringing them 
together into sequences with ideographic characters and radicals to 
*suggest* a specific form of CJK (or other ideographic) character 
assembled from the pieces in a certain order -- but there is no 
implication that a generic text layout process *should* attempt to 
assemble that described character as a single glyph. IDC's are a 
*description* methodology. IDC's are General_Category=So.

The Egyptian quadrat controls, on the other hand, are full-fledged 
Unicode format controls. They do not just describe hieroglyphic quadrats 
-- they are intended to be implemented in text format software and 
OpenType fonts to actually construct and display fully-formed quadrats 
on the fly. They will be General_Category=Cf. Mayan will work in a 
similar manner, although the specification of the sign list and exact 
required set of format controls is not yet as mature as that for Egyptian.

--Ken