Arabic pedagogical symbols non-spacing?

1

In GlyphData.xml I notice that the Arabic characters U+FBB2…U+FBC1 are given a subCategory="Nonspacing"

The Unicode Standard in section 9.2 says specifically:

The range of characters U+FBB2…U+FBC1 provides a set of symbols for this purpose. These are ordinary, spacing symbols with right-to-left directionality. They are not combining marks, …

I understand the need for zero-width versions of nukta glyphs for the purpose of building up composite characters, but I question that such should be encoded as characters that Unicode says are “ordinary, spacing symbols”.

It seems to me that FBB2…FBC1 should be subCategory="Spacing" similar to characters like U+0060 GRAVE ACCENT"

The Unicode Standard goes on to say:

and are not intended for the construction of new Arabic letters by use in combining character sequences.

so it seems to me that whatever is encoded at FBB2…FBC1 should not have anchors such as _top or _bottom since having those invites (perhaps enables) users of the font to try to make new Arabic letters using them.

Bob

2

The Arabic unicode definitions are a bit of a mess to begin with. But I’ll fix this.

Is there a reason why those should be spacing glyphs? What are they intended for?

3

They are Modifiers although Unicode also says FBB2 is a Diacritic.

4

This is a slight rabbit trail unrelated to Glyphs, so feel free to cut off the discussion if desired.

Does Unicode formally define “Diacritic” ? I do not see it anywhere in the Definitions section of Chapter 3 Conformance but maybe I missed it?

In any case, where does Unicode declare FBB2 is a Diacritic?

5

I should have said “Unicode Checker”. It’s under the Misc tab at the bottom for FBB2. Sorry for the omission.

Unicode 6.0 and later has this entry:
Arabic pedagogical symbols
These are spacing symbols representing Arabic letter
diacritics considered in isolation, as for example as in
discussions about the Arabic script.