L2/07-341

Date: Sat, 6 Oct 2007
Source: "Mark Davis
Subject: Deprecating Stateful Controls

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Section 5.20 is woefully out of date. In the subsection "Stateful Format
Controls" (p 194), it recommends that software always maintain stateful
controls in pairs. However, in practice, I know of no software anywhere that
checks every deletion for tag characters or other stateful controls and does
a fixup as Section 5.20 requires. Moreover, if a process doesn't support
character X, it is certainly certainly not going to look for stateful
matching pairs for X and do the fixup. So anytime a process that doesn't
support stateful controls handles text, the stateful controls can be broken.
So there is no way that we can expect software to do the advice in Section
5.20.

We made the annotation and bidi controls robust in terms of specifying
behavior that allows for "broken blocks", exactly because of this issue. The
other stateful controls are still at issue: some of them are already
deprecated, and the others should be. We should:

1. Retract the advice in subsection "Stateful Format Controls" (p 194),
   and replace it by recommendations to
	1. avoid any stateful controls except for bidi and annotation
	   characters, and
	2. if the others are used despite that advice, then the software
	   needs to be cognizant of the fact that unmatched pairs will occur.
2. At long last, deprecate the tag characters. This does not
   mean that people can't use them, but does allow software to detect them
   using Unicode properties (http://unicode.org/Public/UNIDATA/PropList.txt, see "Deprecated").

-- 
Mark