Can an html element have multiple ids?

Question

I understand that an id must be unique within an HTML/XHTML page.

My question is, for a given element, can I assign multiple ids to it?

        
                      

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Answer 1

Contrary to what everyone else said, the correct answer is YES

The Selectors spec is very clear about this:

If an element has multiple ID attributes, all of them must be treated as IDs for that element for the purposes of the ID selector.Such a situation could be reached using mixtures of xml:id, DOM3 Core, XML DTDs, and namespace-specific knowledge.

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Edit

Just to clarify: Yes, an XHTML element can have multiple ids, e.g.

<p id="foo" xml:id="bar">

but assigning multiple ids to the same id attribute using a space-separated list is not possible.

Answer 2

http://www.w3.org/TR/REC-html40/struct/global.html#h-7.5.2

The id attribute assigns a unique identifier to an element (which may be verified by an SGML parser).

and

ID and NAME tokens must begin with a letter ([A-Za-z]) and may be followed by any number of letters, digits ([0-9]), hyphens ("-"), underscores ("_"), colons (":"), and periods (".").

So "id" must be unique and can't contain a space.

Answer 3

That's interesting, but as far as I know the answer is a firm no. I don't see why you need a nested ID, since you'll usually cross it with another element that has the same nested ID. If you don't there's no point, if you do there's still very little point.

Answer 4

My understanding has always been:

• ID's are single use and are only applied to one element...

  • Each is attributed as a Unique Identifier to (only) one single element.

• Classes can be used more than once...

  • They can therefore be applied to more than one element, and similarly yet different, there can be more than one class (i.e. multiple classes) per element.

Answer 5

No you cannot have multiple ids for a single tag, but I have seen a tag with a name attribute and an id attribute which are treated the same by some applications.

Answer 6

No. While the definition from w3c for HTML 4 doesn't seem to explicitly cover your question, the definition of the name and id attribute says no spaces in the identifier:

ID and NAME tokens must begin with a letter ([A-Za-z]) and may be followed by any number of letters, digits ([0-9]), hyphens ("-"), underscores ("_"), colons (":"), and periods (".").