- From: Erik Corry <erik.corry@gmail.com>
- Date: Fri, 2 Mar 2012 10:13:38 +0100
- To: Glenn Adams <glenn@skynav.com>
- Cc: "Phillips, Addison" <addison@lab126.com>, Mark Davis ? <mark@macchiato.com>, Cameron McCormack <cam@mcc.id.au>, "public-script-coord@w3.org" <public-script-coord@w3.org>, Brendan Eich <brendan@mozilla.com>, Anne van Kesteren <annevk@opera.com>, "mranney@voxer.com" <mranney@voxer.com>, es-discuss <es-discuss@mozilla.org>
2012/3/2 Glenn Adams <glenn@skynav.com>: > > On Fri, Mar 2, 2012 at 12:58 AM, Erik Corry <erik.corry@gmail.com> wrote: >> >> 2012/3/1 Glenn Adams <glenn@skynav.com>: >> >> I'd like to plead for a solution rather like the one Java has, where >> >> strings are sequences of UTF-16 codes and there are specialized ways >> >> to iterate over them. Looking at this entry from the Unicode FAQ: >> >> http://unicode.org/faq/char_combmark.html#7 there are different ways >> >> to describe the length (and iteration) of a string. The BRS proposal >> >> favours #2, but I think for most applications utf-16-based-#1 is just >> >> fine, and for the applications that want to "do it right" #3 is almost >> >> always the correct solution. Solution #3 needs library support in any >> >> case and has no problems with UTF-16. >> >> >> >> The central point here is that there are combining characters >> >> (accents) that you can't just normalize away. Getting them right has >> >> a lot of the same issues as surrogate pairs (you shouldn't normally >> >> chop them up, they count as one 'character', you can't tell how many >> >> of them there are in a string without looking, etc.). If you can >> >> handle combining characters then the surrogate pair support falls out >> >> pretty much for free. >> > >> > >> > The problem here is that you are mixing apples and oranges. Although it >> > *may* appear that surrogate pairs and grapheme clusters have features in >> > common, they operate at different semantic levels entirely. A solution >> > that >> > attempts to conflate these two levels is going to cause problems at both >> > levels. A distinction should be maintained between the following levels: >> > >> > (1) encoding units (e.g., UTF-16 coding units) >> > (2) unicode scalar values (code points) >> > (3) grapheme clusters >> >> This distinction is not lost on me. I propose that random access >> indexing and .length in JS should work on level 1, > > > that's where we are today: indexing and length based on 16-bit code units > (of a UTF-16 encoding, likewise with Java) Not really for JS. Missing parts in the current UTF-16 support have been listed in this thread, eg in Norbert Lindenberg's 6 point prioritization list, which I replied to yesterday. >> and there should be >> library support for levels 2 and 3. In order of descending usefulness >> I think the order is 1, 3, 2. Therefore I don't want to cause a lot >> of backwards compatibility headaches by prioritizing the efficient >> handling of level 2. > > > from a perspective of indexing "Unicode characters", level 2 is the correct > place; Yes, by definition. > level 3 is useful for higher level, language/locale sensitive text No, the Unicode grapheme clustering algorithm is not locale or language sensitive http://unicode.org/reports/tr29/#Grapheme_Cluster_Boundaries > processing, but not particularly interesting at the basic ES string > processing level; we aren't talking about (or IMO should not be talking > about) a level 3 text processing library in this thread; I will continue to feel free to talk about it as I believe that in the cases where just indexing by UTF-16 words is not sufficient it is normally level 3 that is the correct level. Also, I think there should be support for this level in JS as it is not locale-dependent. -- Erik Corry
Received on Friday, 2 March 2012 09:14:28 UTC