- From: Chris Lilley <chris@w3.org>
- Date: Wed, 13 Mar 2002 14:50:04 +0100
- To: geoff freed <geoff_freed@wgbh.org>
- CC: www-tt-tf@w3.org, w3c-wai-pf@w3.org
On Monday, 11 March, 2002, 16:45:23, geoff wrote: gf> The timed-text requirements document has been updated; the new gf> version is available at gf> http://www.w3.org/AudioVideo/timetext.html The grouping in terms of Display, Timing, and Architecture is a good one but should Architecture not be presented first? Also, points I.2 and I.3 (see my previous message) belong more clearly under architecture than Display. I.4 is open to misinterpretation as there are special Unicode characters that function as bidi overrides. I suspect that this point is not calling for their use (markup, instead, should be used) but rather, saying that the display of bidirectional text must be supported. Which, for a single level of embedding, such as some rtl characters in the middle ofd a string of ltr characters, is accomplished merely by the existence of such characters. Explicit markup is only required to support multiple levels of embedding (ltr string nested inside rtl string nested inside ltr string). Is that correct? I.6 Expresses both a requirement and a solution, but presents it as an example implying that there are a multitude of possible ways to do the same thing. Thats good in a requirements document, but might be mis-read as 'there will be multiple ways/no defined way in the ensuing specification'. Thus, if it is already agreed that the format will use XML, I suggest rewording as "Allow the language of the text to be identified and text in different languages to be appropriately styled, using xml:lang". This is because xml:lang is already defined in the XML 1.0 specification and is well understood; and because having a single way to identify language increases interoperability, and because CSS has specific selectors for the language of text and thus, for example, color coding or font style changes or whatever can easily be used to denote language in the presentation. This is another requirement that might be better moved to Architecture. In that case, it could be split - this part in Architecture: "Allow the language of the text to be identified using xml:lang" this in Display: "Allow text in different languages to be appropriately styled" I.10 can be read in several ways. a) small graphics can be mixed in with the text, the author having complete control over the content and form of the graphic and the set being open ended. b) a defined set of graphical symbols can be mixed in with the text. The appearance of these symbols is defined precisely in the specification c) a defined set of graphical symbols can be mixed in with the text. The general appearance of these symbols is defined in the specification, the exact appearance being implementation dependent. d) a small, defined set of characters not in Unicode will be supported; their appearance depends on the fonts used to display them which must be provided on a case by case basis. e) a small, defined set of characters not in Unicode will be supported by defining positions in the private use area; their appearance depends on the fonts used to display them. It was not clear to me what I.11 means - does this refer to user preferences as expressed, for example, through a CSS user stylesheet? I understand what point II.2 is getting at, but speaking of 'erasure' is problematic unless it is assumed that all text will be displayed against its own rectangular, opaque background. Rather than thinking of text overwriting other text, I suggest thinking more along the SMIL model that elements have a duration. Between their start and end times, they are visible. Thus, having an old caption disappear and no new caption displayed simply arises as a natural consequence of the architecture. Thuis would help simplify and define buth II.1 and II.2 II.3 and II.4 could be read as contradicting one another on first reading. I suspect that II.3 means that in the markup, the text and its associated timing should be closely associated so that content can be easily re-purposed and easily understood. I suspect that II.4 means that in the specification, the markup for text and the markup for timing will be defined in separate modules, for example to allow a non-timed text format or a timed-something-else format to be developed by others, re-using these modules. Point III.6 seems to call for indexability, in other words to be able to start a timed presentation at any point in the timeline (seek to a point in the timeline; start subtitles half way through a film). I agree, and note that SMIL can do this. III.7 seems to call for multiple language text only one branch of which is displayed (such as the users preferred language) and II.8 for multiple language text all of which is presented, such as a quotation in one language in the middle of text of a different language. I agre with both requirements, but III.8 seems to follow as a natural consequence of I.2,I.3 and I.6. This might be more apparent if, as suggested, those three are moved to section III Architecture. In II.9, assuming this will not be an SGML format, the HTML a element will not be directly possible. I suggest reference be made to the XML possibilities only - the XHTML a element, the SVG a element, generic XLink attributes on a timed-text element, etc. Its not clear to me what III.10 would mean in practice. II.13 suggests two methods, one of which is purely presentational, the other of which is more 'semantic' in that it creates named actors or roles. This seems to me to be far preferable. It gives more flexibility in styling and user choice (see I.11) and enhances re-use and aids requirements such as II.14. (by having something clear in the markup which tools such as XSL-T can use to create derived forms). In I.16, of the three W3C Recommendations listed as possibilities for "complex font displays", only SVG provides this capability. MathML describes equations, but does not provide any font display mechanism and XHTML does not provide any display mechanism at all. This requirenmet could do with clarification as to what it actually means: a) Display of equations must be supported b) There is a need for fonts with complex glyphs such as mathematical symbols, multilingual characters, closed-captioning specific symbols, etc. c) something else that I didn't understand .... II.19 is a good requirement. I suggest adding other W3C Recommendations that will be used as a basis, such as XML 1.0, CSS2, SVG 1.0 and so on (although, depending on the timescale envisaged, SVG 1.1 might be more appropriate particularly given the recent 3GPP decisions to make SVG Tiny a mandatory part of MMS, SVG Basic an optional part, to use SMIL Basic, etc). As already noted by Dave Singer, IV.1 contradicts I.9 and perhaps I.12 and I.14. In addition, given III.19 it seems like an unnecessary restriction, as SMIL already gives a means to give motion to text, and SVG uses such facility extensively. A very good requirements document, Geoff, it was a pleasure to review it. Question - what is the visibility of this document, is it member-only or public? -- Chris mailto:chris@w3.org
Received on Wednesday, 13 March 2002 08:51:51 UTC