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HTML5 Rationale document

Monday, May 10th, 2010

I've started a page on the wiki to document the rationale for the decisions made about the HTML specification.

There are two goals for this document:

  1. Explain why things are the way they are
  2. Explain the difference between multiple similar elements by providing example usages.

One person can not possibly write the entire thing so I hope that this becomes a group process where anyone interested can contribute so go sign up, log in, and edit.

Posted in Syntax, WHATWG | 5 Comments »

HTML5 at Last Call

Tuesday, October 27th, 2009

For a brief period today, there were no outstanding e-mails or bugs on the specs, and so I took that opportunity to transition us here at the WHATWG to the next stage of HTML5's development: Last Call! This affects three specs at the WHATWG:

There's also a version of the spec called Web Applications 1.0 (for nostalgic reasons) that has all of the above as well as a number of other specs, namely Web Storage, Web Database, Server-sent Events, and the Web Sockets API and protocol, all together in one document. With the exception of the Web Database spec, they're all now in last call at the WHATWG.

So if you've been waiting to see if someone else would report the problem that you had seen, well, if it's not fixed, they didn't! So you should now send that feedback in yourself.

There's two ways to send feedback. If your feedback is something short and simple, you can just load up the spec in your browser, click on the section with the problem, then type in your message using the review comments box that appears at the bottom of the window, and hit the "Submit Review Comments" button. This works for the HTML5 and Web Applications 1.0 specs. (Thanks to the W3C HTML Working Group for making their bug database available to us for this purpose.)

If your feedback is more elaborate, then you should subscribe to the mailing list and then send your feedback there.

Note: Lest there be any confusion, the W3C HTML WG has not yet transitioned HTML5 to Last Call at the W3C. HTML5 is a joint effort of W3C and WHATWG groups, but we have different issues lists and different criteria for going to Last Call. For more details on the W3C HTML WG's processes, see the W3C HTML WG charter.

Posted in WHATWG | 16 Comments »

Usability testing HTML5

Sunday, October 4th, 2009

Over the past few weeks, Google has been preparing and then running a usability study to test the microdata feature of HTML5.

Methodology

We first created three different variants based on the original microdata proposal:

  1. One based on what the spec said (documentation)
  2. One trying to put types in an explicit itemtype="" attribute and moving "about" to item="", and replacing itemfor="" with just having multiple item=""s with the same name (documentation)
  3. One trying to remove types altogether and using item as a boolean attribute. (documentation)

Our plan was to run six studies, two for each variant, with each participant running through the following steps:

  1. Read and comment on a couple of motivating slides explaining why one would care about microdata
  2. Read the provided documentation for the variant being tested
  3. Look at and comment on the animals example with microdata (variant 2, variant 3)
  4. Exercise: try to extract the data from the "flickr" example (variant 2, variant 3)
  5. Exercise: try to annotate the blog example (variant 2, variant 3)
  6. Exercise: try to annotate the review example (variant 2, variant 3)
  7. Compare and contrast the "yelp" example with microdata to the equivalent of one of the other two variants (variant 2, variant 3)

We made some changes along the way. After the first three, it became clear that "about" was a very confusing term to use for giving the item's global identifier, and so we changed the documentation and examples to use "itemid" instead (which turned out to be much less confusing). Early on we also introduced some documentation text to explain the differences between the variants in the last exercise, because just showing them the two side by side wasn't getting us anything useful (1 to 3, 2 to 1, 2 to 3, 3 to 1).

After our sixth participant canceled on us, we decided to create a fourth variant (documentation) based on what we'd learnt with the first five, and to get two more participants to test this variant specifically. For these participants, we used the following methodology:

  1. Read and comment on a couple of motivating slides explaining why one would care about microdata
  2. Read the provided documentation for the variant being tested
  3. Look at and comment on the animals example with microdata
  4. Exercise: try to extract the data from the "flickr" example
  5. Exercise: try to extract the data from the review example
  6. Exercise: try to annotate the blog example
  7. Exercise: try to annotate the "yelp" example

Conclusions

Some interesting things came out of this study. First, as mentioned above, the term "about" turns out to be highly non-intuitive. I originally took the word from RDFa, on the principle that they knew more about this than I did, but our participants had a lot of trouble with that term. When we changed it to "itemid", there was a marked improvement in people's understanding of the concept.

Second, people were much less confused about types than I thought they would be. In preparing for this study I discussed microdata with a number of people, and I found that one major area of confusion was the concept of types vs the concept of properties. This is why variant 3 has no types: I wanted to find out whether people had trouble with them or not. Well, not only did people not have problems with types, several participants went out of their way to specify the type of an item, for example using the attribute name "type" instead of "item" in variant 1.

It seems that while reasoning about types at the theoretical level is somewhat confusing, it isn't so confusing that the concept should be kept out of the language. Instead, types should just be more explicitly mentioned. This is why we renamed "item" to "itemtype".

Third, people were confused by the scoping nature of the "item" attribute. Some of our participants never understood scoping at all, and most of the participants who understood the concept were still quite confused by the "item" attribute. We were encouraged, however, by one variant 1 participant's sudden enlightenment when they saw variant 3's "itemscope" attribute, and by the reaction of the variant 3 participant to the "itemscope" attribute compared to the reactions that the other two variants' participants had to their "item" attributes. This is why we split "item" into "itemtype" and "itemscope", instead of just using "itemtype".

We found that people who understood microdata's basic features also understood "itemfor", but while we were doing the study, it was pointed out on the WHATWG list that "itemfor" makes it impossible to find the properties of an item without scanning the whole document. This is why we tested the <itemref> idea in variant 4. People were at least as able to understand this as "itemfor".

In general, the changes we made for variant 4 were all quite successful. With one exception, that's what HTML5 now says. The one exception is that I hoisted the "itemid" property to an attribute like "itemtype", based on the argument that if people want to scan a document for the item with a particular "itemid", <itemref> would make it impossible to do it for the property without creating the microdata graph for the entire page.

One thing we weren't trying to test but which I was happy to see is that people really don't have any problems dealing with URLs as property names. In fact, they didn't even complain about URLs being long, which reassured me that microdata's lack of URL shortening mechanisms is probably not an issue.

Overall, this was a good and useful experience. I hope we can use usability studies to test other parts of HTML5 in the future.

Update

(Added based on Twitter feedback.) Some people have asked to see the raw data we collected in this study. I've uploaded the raw files as they were at the end of each participant's one-hour session. This data on its own isn't especially useful; what matters is how the participants reached their conclusions. There are seven hours' worth of video to document that, but we can't publish the video online, since that would be a violation of the legal agreement we have with the participants to protect their privacy.

The study was conducted by one of Google's usability study moderators, and the participants were screened and recruited by a separate team of usability study recruiters specifically for this study. Our criteria were intended to find Web developers who were somewhat comfortable with HTML and who had at most a passing knowledge of the HTML5 effort.

Bear in mind, when looking at the raw data, that the participants had just one hour to go from not knowing about this at all, to being expected to read and write code in a new syntax, with no hints other than the examples and the documentation (which most only glanced at!).

Posted in WHATWG | 7 Comments »

Spelling HTML5

Thursday, September 10th, 2009

What’s the right way to spell “HTML5”? The short answer is: “HTML5” (without a space).

People in the WHATWG community have commonly referred to HTML5 as “HTML5” for quite a while. However, when the W3C HTML WG voted on adopting “Web Applications 1.0” the question about the title said “HTML 5”. Thus, the W3C HTML WG voted to adopt “HTML 5” as the title, but it wasn’t a vote for or against the space but about “HTML” and “5” in contrast to e.g. “Web Applications 1.0”. Anyway, as a result, the spec was retitled literally “HTML 5”.

This lead to inconsistency. Sometimes people kept writing “HTML5” and sometimes “HTML 5” (even on whatwg.org). This kind of inconsistency is bad for branding. The Super Friends pointed this issue out as the first thing they pointed out.

Now both the WHATWG Draft Standard and W3C Editor’s Draft spell it “HTML5”.

Posted in WHATWG | 29 Comments »

Response to “Notes on HTML 5″

Thursday, September 3rd, 2009

The W3C Technical Architecture Group (TAG) is in the process of reviewing HTML 5. Noah Mendelsohn recently posted his initial, personal, not-speaking-on-behalf-of-TAG notes on HTML 5. Here are my initial, personal, not-speaking-on-behalf-of-WHATWG responses.

Limitations of the XML serialization

This may be old news, but I was surprised to see that document.write() is not supported when parsing the XML serialization. This seems to put the nail in the coffin of XML as a serialization format for colloquial HTML. I understand that there are a variety of issues in making a sensible definition of how this would work, but my intuition is that it could be done reasonably cleanly (albeit not with most off-the-shelf XML parsers).

Many, many things helped drive the nail in the coffin of XML as a serialization format for colloquial HTML. This was probably one of them. Others that come to mind:

Other applicable specifications

"Authors must not use elements, attributes, and attribute values for purposes other than their appropriate intended semantic purpose. Authors must not use elements, attributes, and attribute values that are not permitted by this specification or other applicable specifications." This is one of the most important sentences in the entire specification, but it's somewhat vague. If "other applicable specifications" means: any specification that anyone claims is applicable to HTML 5 extension, then we can extend the langauge with most any element without breaking conformance; if "applicable specifications" is a smaller (or empty) set, then this may be saying that HTML 5 has limited (or zero) extensibility.

The phrase "or other application specifications" is indeed quite important, and quite intentional. It explicitly allows something that previous HTML specifications only implicitly allowed, or disallowed-but-everyone-ignored-that-part: future specifications which extend the vocabulary of previous specifications. Ian Hickson uses RDFa as an example: "If an RDFa specification said that text/html could have arbitrary xmlns:* attributes, then the HTML5 specification would (by virtue of the above-quoted sentence) defer to it and thus it would be allowed. ... Of course, if a community doesn't acknowledge the authority of such a spec, and they _do_ acknowledge the authority of the HTML5 spec, then it would be (for them) as if that spec didn't exist. Similarly, there might be a community that only acknowledges the HTML4 spec and doesn't consider HTML5 to be relevant, in which case for them, HTML5 isn't relevant. This is how specs work."

In response to a question about how validators could possible work with such flexible constraints, Ian Hickson writes, "The same way validators work now. The validator implementors decide which specs they think are relevant to their users. The W3C CSS validator, for instance, can be configured to check against CSS2.1 rules or against SVG rules about CSS. It can't be configured to check against CSS2.1 + the :-moz-any-link extension, because the CSS validator implementors have decided that CSS2.1 and SVG are relevant, but not the Mozilla CSS extensions. ... The W3C HTML validator, similarly, supports checking a document against XHTML 1.1, or XHTML + RDFa, or XHTML + SVG, but doesn't support checking it against XHTML + DOCBOOK. So its implementors have decided that RDFa, SVG, and XHTML are relevant, but DOCBOOK is not."

People who think that such lack of constraints can only lead to madness go strangely silent when it is pointed out that they have already violated such constraints, and the world failed to end as a result.

URL terminology

The HTML 5 draft uses the term URL, not URI.

I was under the impression that HTML 5 uses the term "URL" because that's what everyone else in the world uses (outside a few standards wonks who know the difference between URLs, URIs, IRIs, XRIs, LEIRIs, and so on). A few minutes of research supported my impression. Quoth Ian Hickson: "'URL' is what everyone outside the standards world calls them. The few people who understand what on earth IRI, URN, URI, and URL are supposed to mean and how to distinguish them have demonstrated that they are able to understand such complicated terminology and can deal with the reuse of the term 'URL'. Others, who think 'URL' mean exactly what the HTML5 spec defines it as, have not demonstrated an ability to understand these subtleties and are better off with us using the term they're familiar with. The real solution is for the URI and IRI specs to be merged, for the URI spec to change its definitions to match what 'URL' is defined as in HTML5 (e.g. finally defining error handling as part of the core spec), and for everyone to stop using terms other than 'URL'."

It should be noted that not everyone agrees with this. For example, Roy Fielding (who obviously understands the subtle differences between URLs and other things) recently stated: "Use of the term URL in a manner that directly contradicts an Internet standard is negligent and childish. HTML5 can rot until that is fixed." Maciej Stachowiak, recently appointed co-chair of the W3C HTML Working Group, recently stated: "We need to get the references in order first, because whether HTML5 references Web Address, or IRIbis, or something else, makes a difference to what we'll think about the naming issue. We need to decide as a Working Group if it's acceptable to use the term URL in a different way than RFC3986 (while making the difference clear). If it's unacceptable, then we need to propose an alternate term."

As the old saying goes, "There are only two hard problems in Computer Science: cache invalidation and naming things." I personally don't care about the matter either way, but there is obviously a wide spectrum of opinion.

IRI-bis

It's unclear whether the factoring to reference WebAddr and/or IRI-bis will be retained.

"WebAddr" refers to Web Addresses, a now-defunct proposal to split out the definition of "URL" that HTML 5 uses (which intentionally differs from the "official" definition in order to handle existing web content). The work on the "Web Addresses" specification has now been rolled into IRI-bis; "bis" means "next," so "IRI-bis" means "the next version of the IRI specification." According to Ian Hickson, so important definitions were lost in the process of splitting out "Web Addresses" from HTML 5 and subsequently merging "Web Addresses" into IRI-bis. There is also some feedback about newlines within URLs.

Work on IRI-bis is ongoing. As it relates to HTML 5, it is tracked as HTML ISSUE-56.

Content sniffing

HTML 5 calls for user agents to ignore normative Content-type in certain cases.

HTML 5 calls for user agents to ignore normative Content-Type in certain cases because this is required to handle existing web content. Based on [PDF] the research of Adam Barth and others into the content sniffing rules of a certain closed-source market-dominating browser, progress has been made towards reducing the amount of content sniffing on the public web. (Counterpoint: two steps forward, one step back.)

Personally, I have long been opposed to content sniffing, but if sniffing is going to occur, I would vastly prefer documented algorithms to undocumented ones. The "hope" behind documenting the sniffing rules now is that the web community can "freeze" the rules now and forever, i.e. not add any more complexity to an already complex world. I am personally skeptical, since HTML 5 also introduces (or at least promotes-to-their-own-elements) two new media families, audio and video, for which undocumented or underdocumented sniffing may already occur within proprietary browser plug-ins. And with @font-face support shipping or on the verge of shipping in multiple browsers, there may be new sniffing rules introduced there as well. I hope my concerns are unfounded.

Still, having sniffing rules documented in HTML 5 may -- someday soon -- reduce the complexity of a shipping product. And how often does that happen?

Willful violations

HTML 5 acknowledges in several places that it is in "willful violation" of other specifications from the W3C and IETF.

As stated in §1.5.2 Compliance with other specifications, "This specification interacts with and relies on a wide variety of other specifications. In certain circumstances, unfortunately, the desire to be compatible with legacy content has led to this specification violating the requirements of these other specifications. Whenever this has occurred, the transgressions have been noted as 'willful violations'."

This is the complete list of "willful violations" in the August 25th W3C Editor's Draft of HTML 5. (The WHATWG draft changes almost daily, whenever a change is checked in.)

  1. §2.5.1 Terminology: "The term "URL" in this specification is used in a manner distinct from the precise technical meaning it is given in RFC 3986. Readers familiar with that RFC will find it easier to read this specification if they pretend the term "URL" as used herein is really called something else altogether. This is a willful violation of RFC 3986."
  2. §2.7 Character Encodings: "The requirement to treat certain encodings as other encodings according to the table above is a willful violation of the W3C Character Model specification, motivated by a desire for compatibility with legacy content." Related bugs: Bug 7444, bug 7453, bug 7215, bug 7381. There was a recent discussion about character encoding, starting with Addison Phillips' feedback on behalf of the I18N working group, with several followups. Some salient quotes: Maciej (Apple, Safari): "Browsers for Latin-script locales pretty much universally use Windows-1252 as the default of last resort. This is necessary to be compatible with legacy content on the existing Web." Mark Davis (Google): "At Google, the encoding label is taken only as a weak signal (a small factor in the heuristic detection). It is completely overwhelmed by the byte content analysis. (There are too many unlabeled pages *and mislabeled pages* for the label to be used as is.)" Henri Sivoven (Mozilla contributor), in response to a question about what constitutes a "legacy environment" for the purposes of character encoding detection: "The Web is a legacy environment." (Ian Hickson echoes this sentiment.)
  3. §2.7 Character Encodings: "The requirement to default UTF-16 to LE rather than BE is a willful violation of RFC 2781, motivated by a desire for compatibility with legacy content."
  4. §3.4 Interactions with XPath and XSLT: "These requirements are a willful violation of the XPath 1.0 specification, motivated by desire to have implementations be compatible with legacy content while still supporting the changes that this specification introduces to HTML regarding which namespace is used for HTML elements."
  5. §3.4 Interactions with XPath and XSLT: "If the transformation program outputs an element in no namespace, the processor must, prior to constructing the corresponding DOM element node, change the namespace of the element to the HTML namespace, ASCII-lowercase the element's local name, and ASCII-lowercase the names of any non-namespaced attributes on the element. This requirement is a willful violation of the XSLT 1.0 specification, required because this specification changes the namespaces and case-sensitivity rules of HTML in a manner that would otherwise be incompatible with DOM-based XSLT transformations. (Processors that serialize the output are unaffected.)" There is a long discussion of these two violations in the comments of bug 7059.
  6. §4.10.16.3 Form submission algorithm: "Step 9: If action is the empty string, let action be the document's address. This step is a willful violation of RFC 3986, which would require base URL processing here. This violation is motivated by a desire for compatibility with legacy content."
  7. §6.5.3 Script processing model: "If the script's global object is a Window object, then in JavaScript, the this keyword in the global scope must return the Window object's WindowProxy object. This is a willful violation of the JavaScript specification current at the time of writing (ECMAScript edition 3). The JavaScript specification requires that the this keyword in the global scope return the global object, but this is not compatible with the security design prevalent in implementations as specified herein."
  8. §12.3.4 Other elements, attributes, and APIs: Regarding document.all, "These requirements are a willful violation of the JavaScript specification current at the time of writing (ECMAScript edition 3). The JavaScript specification requires that the ToBoolean() operator convert all objects to the true value, and does not have provisions for objects acting as if they were undefined for the purposes of certain operators. This violation is motivated by a desire for compatibility with two classes of legacy content: one that uses the presence of document.all as a way to detect legacy user agents, and one that only supports those legacy user agents and uses the document.all object without testing for its presence first."

As you can probably guess from these quotes, the HTML 5 community has decided that compatibility with existing web content trumps all other concerns. Other than the use of the term "URL," all of the "willful violations" are instances where other specifications do not adequately describe existing web content. I personally do not understand most of the issues listed here, so I have no opinion on whether the alleged benefit of violating existing standards is worth the alleged cost.

Versioning

In-band global version identifiers, if new implementations handle them reasonably, may be useful for (a) authoring applications that want to track versions used for authoring (b) informative error handling when applications encounter constructs that are apparently 'in error'.

The idea of version identifiers has been hashed and rehashed throughout the 5+ year process of defining HTML 5. Most notably, Microsoft proposed a version identifer shortly after the W3C HTML Working Group reformed around HTML 5. Their proposal generated much discussion, but was not ultimately adopted. Several months later, Microsoft shipped Internet Explorer 8 with a "feature" called X-UA-Compatible, which serves as a kind of IE-specific version identifier. I am personally not a fan of this approach, in part because [PNG] it adds a lot of complexity for web developers who want to figure out why the still-dominant browser doesn't render their content according to standards.

Versioning in HTML 5 is tracked as HTML ISSUE-4.

Posted in WHATWG | 17 Comments »