Thanks for the clarification. I think the combining mark would not combine with the new line mark but would be a defective combining sequence. I might wish to do this simply because, according to UTR #14 this is the only way to get a combining mark to be treated as AL as I might wish. Probably not the best way to do this, but not illegal!Thanks for the clarification. I probably misunderstood Jon's intention.
But is there a problem if, for example, an application sees the string
<space, space, combining mark> and regularises it (wrongly!) to <space,
combining mark>?
Yes, I was not saying that it wouldn't be sensible to begin a line of text with a spacing diacritic (whether precomposed or created using space or NBSP). I was saying that it wouldn't be sensible to begin a line with a combining diacritic, since that combining diacritic would be combining with a newline character which it's difficult to think of any possible sensible meaning for. Attribute normalisation would change the sequence U+000A, <combining> to U+0020, <combining> which would arguably change the meaning, but changing the meaning of a meaningless construct isn't a problem to my mind.
So it seems to me that this attribute normalisation is a problem. It is a problem for the higher level protocol as thinks it has created a space but in fact it has created a combining sequence which it must not treat as a space. A legal sequence at a lower level, even if meaningful, should not confuse the higher level. (Indeed I don't think the higher level ought to be confused even by illegal sequences at the lower level, it should be transparent as far as possible.) So the higher level protocol needs to know not only not to split a space, combining mark sequence but also not to create one where one was not present before. Perhaps it needs to insert a suitable separator (ZWNJ?) to ensure that when the space is created it is not combined with the combining mark. So another example of needless complication created by the long-standing decision to permit space as a carrier for combining marks.
-- Peter Kirk [EMAIL PROTECTED] (personal) [EMAIL PROTECTED] (work) http://www.qaya.org/
