Philippe Verdy <verdy underscore p at wanadoo dot fr> wrote:
I also found an acute on diphtongs, placed on the boundary of both letters (au, ei, eu, oe, and ui).
Wouldn't such diacritic be hold by the currently proposed invisible base character (in the Public Review section of the Unicode website), by encoding for example: a,INVISIBLE LETTER,combining acute,u If you think there's a grapheme cluster here, I suggest using ZWJ to attach the three default grapheme clusters: a,ZWJ,INVISIBLE LETTER,combining acute,ZWJ,u to create a kerning ligature between the two vowels.
I thought one of the unstated, beneficial side effects of INVISIBLE LETTER was that it might reduce the need for non-intuitive ZWJ and ZWNJ sequences. I may be wrong, though; I haven't followed the INVISIBLE LETTER debate very closely.
In the (short) PR-41 document, the intent is really to substitute the SPACE character by another one to serve as a base character for isolated diacritics. (SPACE is known to cause problems in HTML/XML due to whitespace compression and in text parsers such as word-breakers). It won't deprecate the existing spacing diacritics block, but will avoid adding new spacing variants for the existing or future diacritics that may need them.
The current semantics of SPACE and its reuse to serve as a base for diacritics requires changing the character properties of SPACE when a diacritic follows it, and this is really a bad exception to the general framework where a combining sequence should inherit almost all its properties from its base character. I don't see the proposal as a way to avoid any use of joiners/non-joiners in its current form.
