- From: Maciej Stachowiak <mjs@apple.com>
- Date: Tue, 19 Apr 2011 22:42:12 -0700
- To: Leif Halvard Silli <xn--mlform-iua@xn--mlform-iua.no>
- Cc: Laura Carlson <laura.lee.carlson@gmail.com>, HTMLWG WG <public-html@w3.org>
Yes, we will consider your submission. Thank you for providing additional info. Regards, Maciej On Apr 19, 2011, at 10:00 PM, Leif Halvard Silli wrote: > Hi Maciej, my assumption is that the chairs now are considering the > new info I provided. Do you need more detailed info? When could there > be a reply? > > Meanwhile, hereby follows the outline of a change proposal for the > generator exception. Suggestions for how to improve are much wanted - > send to this list or to list@html4all.org. > > CHANGE PROPOSAL (1st edit): > > A common treatment of all images without @alt. Omittance > without explicit permission is treated as 'invalidateable'. > > SUMMARY: > > 1 Images with omitted @alt for which the validator cannot > determine a condition for which HTML5 has an explicit > permission to omit the @alt, are classified as invalidatable > w.r.t. alternative text rather than as invalid, except when > the validator determines a situation for which HTML5 demands > a specific @alt usage. As HTMl5 already says, documents with > such IMG elements cannot be stamped as conforming. > > 2 Validators are authoring tools. They should thus list/count > all IMG elements with omitted @alt, in following categorizes: > > a) those which do not fall into category b), c), d) or e) > [Thus, for a), then omitted @alt is a de facto per-element > signal that this element cannot be stamped a conforming.] > b) those that are valid e.g. because they are the sole content > inside a figure with figcaption. (In the figure case, then > @alt represents the presence of the image = can be omitted.) > c) those with role=presentation (should have empty alt) > d) those that are the sole content of links (alt = link text) > e) those that fall into any other machine checkable situation > for which it can be given clear advice about what to replace > the omitted alt with. > > NOTE: A basis of this CP is the fact that UAs will and should > be encouraged to - or MUST - repair the lack of @alt > even in cases when it is valid to not have an @alt. This, in > turn, together with a view of the validator as an authoring > tool, is the basis for why validator should account for all > images without @alt. > PS: To ask that UAs not generate @alt when it is valid to drop > it = Accessibility decrease = Useless extra UA requirement. > NOTE: Validator warns that images without @alt (probably) will > have alt text being generated and that many images in category > 2a) above probably will hamper accessibility of the document. > > 3 Introduction of <style>img::alt { content:"Image.";}</style> > > > RATIONALE: > > This CP accepts as a fact that authors and authoring tools will > continue to write invalid documents w.r.t. @alt and that this may need > a more "soft" response than what is common for HTML4 validation. At the > same time, authors who rely on the validator as a authoring tool, need > to be made aware about the errors that prevent the document from being > conforming. And therefore the generator string as a silent error > suppressor is not useful and also introduces a range of additional > problems. [1] Instead we need a single system for every validator > service user. Additionally, HTML5 encourages @alt text to be generated > when @alt is lacking, and this is something that authors need to be > aware of even when - or if - it is valid to omit the @alt. > > DETAILS: > > [ This section should probably be replaced by exact spec text. ] > > 1) Clarification of how UAs should repair the lack of @alt: > > a) for IMG with omitted alt, alt text should be generated > even when the image is not required to have @alt attribute. > E.g. this example *does* need that the @alt text is > repaired for the purpose of representation of the image: > <figure><figcaption>Title</figcaption><img src=* ></figure> > > b) currently the spec only *encourages* such repair text. This > CP suggests a MUST instead. [Comments w.r.t. MUST/SHOULD ?] > > c) ALT text repair text proposal: > * The repair text should be: alt="Image." > * The repair text should be localized. > * The localization should be that of the UA and not > that of the document/element. (Because the user might > read a page that he/she don't understand the language > of. It would also be too much to require UAs to support > the several thousand possible translations of the string > 'Image.' That alt="Image." isn't localized to the > document language, is also a form of encouragement to the > author to actually do provide a useful, localized text.) > * AT treatment of a such generated alt="Image." may vary. > [This may need to be fleshed out.] > (I note that e.g. VoiceOver pronounces 'Image.' for most > non-presentational images that it detects, but that this > is not @alt text but more an element classification. It > may not make sense to say "Image: Image." Hence AT > should be free to not read such repair text.) > * HTML5's warning that authors should not rely on > such repair text should remain as is. > > 2) Introduction of a CSS selector for generating alt text: > img::alt { content:"Image.";} > This would allow the author to let the alt text vary per > document language and things like that. This CSS should have > no bearing on the validity of the image. > > 3) Validators should count all IMG elements with omitted @alt > and list their numbers (or simply list them) as follows: > > a) all IMG elements that are lacking @alt and which > also do not fall into category b), c), d) or e) below. > > * These images should simply be listed (or made account > for by telling how many they are). The validator should > not stamp them as an error. It should instead say that > it did not perform the validation that was asked for with > regard to @alt text = cannot stamp document as conforming. > [This is meant to be in line with HTML5's current > statement that documents with the generator string > are not conforming etc.] > Validator should also state that user agents are > required to generate @alt text for these images. > And it should also state that there is a high probability > that the accessibility of the document is hampered > because of their lack of alt text. > > b) all IMG elements that are valid but without @alt. > > * This is necessary because even when they are valid > without @alt, an @alt text will, nevertheless, be > generated. It is important that authors are made aware of > this consequence of leaving the @alt out: the author may > not be satisfied with the auto-generated alt text - etc. > > c) all IMG elements with role=presentation. > > * for these images, the validator requires that they get an > @alt [whether that @alt MUST or SHOULD be empty, is a > separate question]. This is in line with the current > Decision on this issue. > > d) all IMG elements that are the sole content of a link > > * for these elements, the validator must require an > alt text that is suitable as a link text. This is in > line with what HTML5 currently says about such cases. > > e) any other machine checkable situation for which the > validator would be able to give accurate advice etc. > > 4) Validators, themselves being HTML5-parsers, when they display > the checked/parsed source, MAY display this generated alt > text - preferably in a way which makes the author see that it > is generated. May be the same colour can be used as is used to > for "obsolete but conforming" features. > > 5) Even for documents where all IMG elements are machine checkable > conforming there should be an encouragement to perform detailed > image analysis to verify that the document really is conforming. > > IMPACT: > > Positive effects. > 1) solves the problem the generator exception was meant to solve > 2) treats all validation users the same, authoring tools & authors > 3) avoids having to define/guess what "hand-authored pages" means > 4) can still be used as solution to the "e-mail exception" > 5) offers "quick" validation for those in a hurry without > leaving out the necessary info for those who need the details > 6) avoids that there is is a condition (the generator exception) > under which all the @alt text rules are dropped on the floor > 7) incorporates HTML5's current notion of documents with the > generator string as not conforming but instead says that > this applies to any document where there is an omitted @alt > 8) more pedagogical validator services. Example: An author > inserts the follwoing code in a HTML5 validator: > <a href=link><img src=*></a> > Validator then reports back that the img lacks an alt text that > suitable as a link text. Thus the author has learned, without > reading the spec, that an IMG which is sole content of a link, > should have an @alt text which is suitable as link text. > This is also in line with HTML5's notion that one should not > insert alt text if one doesn't know what to put there: The lack > of @alt then becomes a pretext for the validator to try to give > advice about what to put there. > 9) Author gets statistics about how many images in this and that > category he/she has - this is helpful when trying to get > down to zero invalidatable images. > > Negative effects. > 1) It is still a change compared with HTML4. > 2) Some may prefer more direct error messages. > > CONFORMANCE CLASSES CHANGES > > 1) the special treatment of documents with the generator > string is dropped > 2) validators are required to give detailed responses when > validating IMGs with omitted @alt > 3) spec needs to classify which situations *are* machine checkable > and which situation aren't. Otherwise, different validation > services will not detect the same situations. NB: Important > that the spec can be expanded, in case more machine checkable > situations are detected. > 4) how to stamp documents with invalidatable img elements must > be specced rather well, to avoid possible misuses. > Perfect balance is important. > 5) more detailed spec + requirements w.r.t. @alt text repair > 6) more detailed spec + requirements w.r.t. AT and repaired @alt > 7) spec text with advice about how to use img::alt{}. Could e.g. > say that it can useful whenever it is valid to drop the @alt. > > RISKS > > 1) Risk that validator users do not understand the difference > between a document with invalidatable img elements and fully > conforming documents. > 2) Risk that non-conforming documents are presented as conforming, > against the presenter's better knowledge. (Misuse.) > 3) Risk that img::alt{content:"Alt text";} is misused. > 4) Perhaps authors will drop all @alt text and then run against > the validator, with the aim of only add @alt text for those img > elements where validator requires them? Thus a kind of "satisfy > the validator" behaviour. > 5) too complicated for validator developers? > 6) too complicated validation reports? (Solvable through validation > service design.) > > REFERENCES: > [1] Letter to the chairs with new info re/the generator exception > http://lists.w3.org/Archives/Public/public-html/2011Apr/0466 > > End of CP (1st edit). > > Leif Halvard Silli >
Received on Wednesday, 20 April 2011 05:42:55 UTC