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Re: [selectors4] Behavior undefined for multiple elements sharing the same ID

From: Tab Atkins Jr. <jackalmage@gmail.com>
Date: Mon, 11 Sep 2017 10:47:34 -0700
Message-ID: <CAAWBYDDfWe6J8VX7K8U=6=Nb5asAN5zXM4hY+2-q2yAXyTpWjA@mail.gmail.com>
To: Simon Pieters <simonp@opera.com>
Cc: Sangwhan Moon <sangwhan@iki.fi>, Xidorn Quan <me@upsuper.org>, "www-style@w3.org" <www-style@w3.org>
On Mon, Sep 11, 2017 at 12:23 AM, Simon Pieters <simonp@opera.com> wrote:
> On Mon, Sep 11, 2017 at 8:46 AM, Sangwhan Moon <sangwhan@iki.fi> wrote:
>> > On 11 Sep 2017, at 3:17 PM, Xidorn Quan <me@upsuper.org> wrote:
>> >
>> > On Mon, Sep 11, 2017, at 04:04 PM, Sangwhan Moon wrote:
>> >> While dealing with a strange edge case related to duplicated IDs
>> >> (triggered via cloneNode(), but also can be done by poorly written
>> >> markup) I noticed that the selectors spec doesn't define what
>> >> implementations are expected to do when there are multiple elements
>> >> which
>> >> define the same ID.
>> >
>> > The spec makes it pretty clear that all elements with the same ID should
>> > be
>> > matched.
>> >
>> > The spec says:
>> >> An ID selector represents an element instance that has an identifier
>> >> that
>> >> matches the identifier in the ID selector.
>> > and it specifically mentions the case after:
>> >> (It is possible in non-conforming documents for multiple elements to
>> >> match
>> >> a single ID selector.)
>>
>> Oh, I completely missed that statement between the parentheses. Thanks.
>>
>> I was referring to this bit: "whatever the document language, an ID typed
>> attribute can be used to uniquely identify its element." - my confusion
>> mostly comes from the fact that unique IDs for conformance is implied in
>> HTML at the moment, but is not enforced (and from what I gather, not defined
>> either - which makes it a bit unclear if it duplicate IDs is against
>> conformance or not.) - I suppose that's something I need to bring up with
>> HTML and report back what is actually a conforming document in this context.
>
>
> "When specified on HTML elements, the id attribute value must be unique
> amongst all the IDs in the element's tree and must contain at least one
> character. The value must not contain any ASCII whitespace."
>
> https://html.spec.whatwg.org/multipage/dom.html#the-id-attribute

Yeah, CSS *expects* that IDs are singular in the document, but defines
how the ID selector works regardless; and HTML defines that a valid
document has unique IDs (but also defines how its own things work
regardless).

~TJ
Received on Monday, 11 September 2017 17:48:18 UTC

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