On 6/14/20 4:57 PM, Corentin Jabot wrote:


On Sun, 14 Jun 2020 at 22:45, Jens Maurer <Jens.Maurer@gmx.net> wrote:
On 14/06/2020 22.19, Corentin Jabot wrote:
>
>
> On Sun, 14 Jun 2020 at 21:55, Jens Maurer <Jens.Maurer@gmx.net <mailto:Jens.Maurer@gmx.net>> wrote:

>     No, each code point in a sequence (given Unicode input) is a separate abstract character
>     in my view (after combining surrogate pairs, of course).
>
>
> For example diatrics, when preceded by a letter are not considered abstract characters of their own.

"Abstract character" is defined in https://www.unicode.org/glossary/ as follows:

"A unit of information used for the organization, control, or representation of textual data."
(ISO 10646 does not appear to have a definition in its clause 3.)

I'm not seeing a conflict between that definition and my view that a diacritic,
preceded by a letter, can be viewed as two different abstract characters.
I agree that the alternate viewpoint "single abstract character" is not
in conflict with the definition, either.

What is your statement "are not considered abstract characters of their own"
(which seems to leave little room for alternatives) based on?

Right the glossary, is very much incomplete

The definition is given in Unicode 13. 3.4 ( http://www.unicode.org/versions/Unicode13.0.0/ch03.pdf ) 

Abstract character: A unit of information used for the organization, control, or representation of textual data.
• When representing data, the nature of that data is generally symbolic as
opposed to some other kind of data (for example, aural or visual). Examples of
such symbolic data include letters, ideographs, digits, punctuation, technical
symbols, and dingbats.
• An abstract character has no concrete form and should not be confused with a
glyph.
• An abstract character does not necessarily correspond to what a user thinks of
as a “character” and should not be confused with a grapheme.
• The abstract characters encoded by the Unicode Standard are known as Unicode abstract characters.
• Abstract characters not directly encoded by the Unicode Standard can often be represented by the use of combining character sequences.

My reading of that aligns with Jens' interpretation.  An abstract character can be composed from abstract characters.  The emphasized statement above appears to reaffirm that.

The definition of encoded character is also informative

 Encoded character: An association (or mapping) between an abstract character and a code point.
• An encoded character is also referred to as a coded character.
• While an encoded character is formally defined in terms of the mapping
between an abstract character and a code point, informally it can be thought of
as an abstract character taken together with its assigned code point.
Occasionally, for compatibility with other standards, a single abstract character
may correspond to more than one code point—for example, “Å” corresponds
both to U+00C5 Å latin capital letter a with ring above and to U+212B
Å angstrom sign.
• A single abstract character may also be represented by a sequence of code
points—for example, latin capital letter g with acute may be represented by the
sequence <U+0047 latin capital letter g, U+0301 combining acute
accent>, rather than being mapped to a single code point.


Likewise here, these examples indicate that an abstract character may have multiple encoded representations, but I don't read this as precluding the indicated code points reflecting abstract characters on their own.

Tom.