Focus behavior in HTML had been under-specified for the past few years, and it was also quite confusing due to a variety of subtle differences between focusing methods, UA-specific behaviors, relation to the tabindex attribute, relations to shadow DOM, etc.
A few months ago Domenic filed a meta-bug that contains a list of things to fix so that we would have a good foundation for further additions to focus-related stuff, and to hopefully make focus in HTML make sense to browser engineers and web authors!
Types of focus
You may know that you can focus on stuff by clicking on them, tabbing, or calling focus() on it — but did you know that things might be focusable with one method but not with others? Domenic and Mu-An made a giant interactive list of HTML elements to showcase how they react to different methods of focusing, and can be tested from various browsers to show the difference between them.
To reflect the varying behaviors of focus in various UAs in the spec, we classified focusability into three types: “programmatically focusable”, “click focusable”, and “sequentially focusable”.
If an element is programmatically focusable, it will get focused when calling the focus() method on it or when putting an autofocus attribute on the element. In all platforms, all elements that are either click focusable or sequentially focusable are also programmatically focusable, so “programmatically focusable” is interchangeable with “focusable”.
If an element is click focusable, the element will get focused when it’s clicked. This has the same set of elements as “programmatically focusable” in most UAs/platforms. A notable exception is Safari where non-editable form controls (checkboxes, etc.) are not click focusable by default.
If an element is sequentially focusable, the element can be focused through “tabbing” — in most UAs this means pressing Tab/Shift+Tab (and in Safari, Option+Tab too!).
Previously the spec didn’t clearly differentiate “programmatically focusable” and “sequentially focusable”, didn’t even mention “click focusable”, and used the “tabindex focus flag” concept which was slightly confusing due to its relations with the tabindex attribute. So we updated it in this PR.
As you may know already, built-in elements like <button>, <input>, <a>, etc. all have a “default” focus behavior — they are focusable (or not) by default. When the tabIndex property getter is run on an element whose tabindex attribute is not explicitly set already, it will return 0 sometimes and -1 other times. Previously, the spec said to return 0 if the element is “focusable” by default (which type of focusable?), and -1 otherwise. But this wasn’t implemented anywhere, because of possible differences in which elements are focusable by default in various UAs. So now the spec actually checks if the tag name is one of the tag names included in a pre-defined list. This is quite awkward, but at least it’s interoperable! (PR is here.)
Now, what is the use of tabindex exactly? You can make an element focusable by setting its tabindex attribute to an integer. This will set the tabindex value, and thus impact the focusability of the element. If the integer is non-negative, the element is also sequentially focusable. You can’t, however, make an element not focusable at all through this attribute — there is no value you can set the tabindex attribute to on a <button> that will stop it from being focusable.
You can also modify the order of elements traversed with sequential navigation/tabbing — elements with a positive tabindex value will be traversed first, in ascending order (and in tree order in case of a tie), and then elements with a tabindex value of zero (or unspecified but the element is sequentially focusable by default), in tree order.
The autofocus content attribute is useful if you want to set focus on a form control element on page load. However, it had some issues such as:
The autofocus attribute was available only for some form control elements, and unavailable for other focusable elements like <summary>, <div contenteditable="true">, and <span tabindex="0">.
The behavior with an autofocused element in a page accessed with a fragment identifier (e.g. https://example.com/#foo) was not interoperable.
What should happen if there are multiple autofocused elements, and one of them is not focusable?
The HTML specification and the SVG specification were updated to resolve these issues by changes 1, 2, and 3. Now the autofocus content attribute and the autofocus IDL attribute are available on all HTML and SVG elements. The autofocus content attribute is not processed if its document has a fragment identifier, or has a focused element. If an autofocus element is not focusable, the element is skipped and another autofocus element is handled.
Shadow DOM and delegatesFocus
All of the previously mentioned concepts were already specced in the HTML spec in some way, albeit a bit unclear, not reflecting the actual behavior, etc. Focus behavior with shadow DOM, though, had not been upstreamed from the old Shadow DOM spec at all, so this part of the effort took the most time overall. Since some parts of the Shadow DOM spec on focus were unclear and needed more explanation, we also took a look at how it’s implemented in Blink to get the exact behavior down, and discussed with other browser vendors and web developers on whether we want to keep the implemented behavior or not in some cases.
A new concept added (PR 1, 2) by Shadow DOM is “delegates focus”, which is used when you want attempts to focus on a shadow host to not focus on the host itself, and instead delegate the focus to within the shadow tree (like <input type="date">!). In Blink, this delegation uses the sequential focus navigation order, but we think it is a bit weird and started a discussion on how this should actually work — finally changing the delegation to respect the protocol of whatever the focusing method is originally used. (That is, use sequential order if we used tabbing, otherwise use flat-tree order and respect click focusability if needed.)
Now that we have a good-enough spec for focus, we have a good foundation for future additions to focus. One new relevant proposal is “custom element default focusability”. As we’ve mentioned, built-in elements have a “default” focus behavior — even though they don’t have a tabindex value explicitly, they are still focusable (or not). When you’re making custom elements, though, currently there is no way to make them focusable by default, without setting the tabindex attribute. The proposal listed various ways this might be solved, and it was talked about in TPAC with a relatively positive response from various parties. Do check it out if you’re interested!
In summary, focus was and is still quite complex to understand. But, at least now there’s a clear source of truth for it, and the browser vendors are working to make it interoperable — implementing new changes to the spec as soon as they can. There are still lots of focus-related things that need to be specced (we’ve heard people mention focusin/focusout, more CSS selectors, etc.), so if you’re intrigued by this post, know that you can also contribute to fix more things like these!
Having an old and mostly confusing focus spec, different types of focus, and multiple uses for tabindex made things quite complicated when starting out. However, one of the trickiest parts of focus, in my opinion, is the fact that what is focusable/click focusable/sequentially focusable might differ in different UAs, and it might be dynamic as well! (E.g. in Safari what’s sequentially focusable changes if you hold down the Option key!) This means we need to make sure the spec is written to allow for differences, but is still, um, specific enough to make things not too ambiguous.
Overall, we’re happy with the result of this effort. We’d like to thank all the parties involved that participated in various ways: experimenting, reviewing spec PRs, implementing the changes, commenting/participating in discussions, etc. Special thanks to Kent Tamura (who wrote some parts of this post and did the autofocus specs) and Domenic Denicola (who kickstarted this whole effort, reviewed all the PRs, and suggested + reviewed this post).
Now we can focus on other parts of HTML Standard...
Based on a query of the HTTP Archive data set, containing the raw content of the top 1.3 million web pages, we find the relative usage of each HTML element. The fieldset element is used on 8.41% of the web pages, which is higher than other popular features, such as the video and canvas elements; however, the legend element is used on 2.46% of web pages, which is not ideal for assistive technologies. Meanwhile, the form element appears on 70.55% of pages, and we believe that if interoperability bugs were fixed, correct and semantic fieldset and legend use would increase, and have a positive impact on form accessibility for the web.
Fieldset standards history
In January 1997, HTML 3.2 introduces forms and some form controls, but does not include the fieldset or legend elements.
The FIELDSET element allows form designers to group thematically
related controls together. Grouping controls makes it easier for users
to understand their purpose while simultaneously facilitating tabbing
navigation for visual user agents and speech navigation for
speech-oriented user agents. The proper use of this element makes
documents more accessible to people with disabilities.
The LEGEND element allows designers to assign a caption to a FIELDSET.
The legend improves accessibility when the FIELDSET is rendered
non-visually. When rendered visually, setting the align attribute on
the LEGEND element aligns it with respect to the FIELDSET.
In December 1999, HTML 4.01 is published as a W3C Recommendation, without changing the definitions of the fieldset and legend elements.
Of the 26 issues filed against the specification, 17 are about rendering interoperability. These rendering issues affect use cases such as making a fieldset scrollable, which currently result in broken scroll-rendering in some browsers. These issues also affect consistent legend rendering which is causing web developers avoid using the fieldset element altogether. Since the fieldset element is intended to help people who use assistive technologies to navigate forms, the current situation is less than ideal.
HTML spec rendering issues
In April of this year, Mozilla developers filed a meta-issue on the HTML specification “Need to spec fieldset layout” to address the ambiguities which have been leading to interoperability issues between browser implementations. During the past few weeks of work on fieldset, we made initial proposed changes to the rendering section of the HTML standard to address these 17 issues. At the time of this writing, these changes are under review.
Proposal to extend -webkit-appearance
Web developers also struggle with changing the default behaviors of fieldset and legend and seek ways to turn off the “magic” to have the elements render as normal elements. To address this, we created a proposal to extend the -webkit-appearance CSS property with a new value called fieldset and a new property called legend that are together capable giving grouped rendering behavior to regular elements, as well as resetting fieldset/legend elements to behave like normal elements.
The general purpose proposed specification for an "unprefixed" CSS ‘appearance’ property, has been blocked by Mozilla's statement that it is not web-compatible as currently defined, meaning that implementing appearance would break the existing behavior of websites that are currently using CSS appearance in a different way.
We asked the W3C CSS working group for feedback on the above approach, and they had some reservations and will develop an alternative proposal. When there is consensus for how it should work, we will update the specification and tests accordingly.
We had also considered defining new display values for fieldset and legend, but care needs to be taken to preserve web compatibility. There are thousands of pages in HTTP Archive that set ‘display’ to something on fieldset or legend, but browsers typically behave as display: block was set. For example, specifying display: inline on the legend needs to render the same as it does by default.
The WebKit and Edge teams are aware of bugs, and we will follow up with them to track progress.
The fieldset and legend elements are useful to group related form controls, in particular to aid people who use assistive technologies. They are currently not interoperable and are difficult for web developers to style. With our work and proposal, we aim to resolve the problems so that they can be used without restrictions and behave the same in all browser engines, which will benefit browser implementers, web developers, and end users.
I gave a talk at Google on Monday demonstrating the various features of HTML5 that are implemented in browsers today. The video is now on YouTube, so now you too can watch and laugh at my lame presentation skills!
The segments of this talk are as follows. Some of the demos are available online for you to play with and are linked to from the following list:
If you're very interested in watching my typos, the high quality version of the video on the YouTube site is clear enough to see the text being typed. More details about the demos can be found on the corresponding demo page.
implementation of Web
has been released. The W3C HTML Working Group is now
reviewing the Web Forms 2.0 specification to serve as a
basis for the next version HTML (as everyone knows). Some discussion on
the HTML WG mailing
list regarding the WF2 specification has been at times ignorant of the
content of the specification and what it actually enables authors to
Hopefully by using this implementation and examining its associated test
the meaning of the specification will be clarified, and members of the
HTML WG will be more educated so as to more constructively review it.
I started work on this project with an standalone
implementation of the repetition model, but I have since expanded it to
include other WF2 features as well. I developed this library on the job
for incorporation into the various development projects I was working
on; I have found the functionality provided by WF2, especially the
repetition model and the form validation model, to greatly ease
development. Try using it in your own projects and see for
yourself, and then drop a line to WHATWG and the HTML WG with
your feedback on what works well and what needs to be improved.
This implementation works in Firefox 1+, MSIE 6+, and Safari
of course, has a native implementation). For more information on the implemented features, see the implementation
details. This implementation will follow the HTML 5
specification that evolves from the work done by the HTML Working Group.
this post refers to the "Write" interface from WordPress utilized to post comments to WHATWG blogs.
there is well-intentioned, but mis-implemented markup in the edit form; namely, improper implemetation of the FIELDSET.
for a proper FIELDSET, one needs to do 4 things:
open the FIELDSET (which this form does)
define a LEGEND for the FIELDSET (which this form does NOT); the natural candidates for LEGEND are the level 3 headers (H3) classed dbx-handle so instead of repeatedly hearing "click to open this box", i would also get the pseudo-box (which i would call sub-forms) LEGEND as an indicator of what i am about to open or close. i would also make the alt text device independent - instead of "click here to open this box", i would propose "show sub-form" and "hide sub-form"
bind individual FORM controls to their textual labels by use of the LABEL element and the for/id mechanism that ties the form control (which takes the "id") to a LABEL (which takes the "for") or multiple labels; the LABELshould contain the actual, textual label, and NOT the FORM control, as in this form; this form has the attribute set set correctly to bind the LABEL to the FORM control, but since the LABEL element is opened PRIOR to the INPUT element, no labeling is available to the user - in my case (i use a screen-reader) the sub-forms that appear when one opens a FIELDSET to reveal a FORM appear unlabeled to my screenreader, because of invalid markup.