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?
<div id="nested_element_123 task_123"></div>
I realize I have an easy solution with simply using a class. I'm just curious about using ids in this manner.
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.
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.
From the XHTML 1.0 Spec
In XML, fragment identifiers are of type ID, and there can only be a single attribute of type ID per element. Therefore, in XHTML 1.0 the id attribute is defined to be of type ID. In order to ensure that XHTML 1.0 documents are well-structured XML documents, XHTML 1.0 documents MUST use the id attribute when defining fragment identifiers on the elements listed above. See the HTML Compatibility Guidelines for information on ensuring such anchors are backward compatible when serving XHTML documents as media type text/html.
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 (".").*
No. Every DOM element, if it has an id, has a single, unique id. You could approximate it using something like:
<div id='enclosing_id_123'><span id='enclosed_id_123'></span></div>
and then use navigation to get what you really want.
If you are just looking to apply styles, class names are better.
My understanding has always been:
ID's are single use and are only applied to one element
Classes can be used more than once
No, you should use nested DIVs if you want to head down that path. Besides, even if you could, imagine the confusion it would cause when you run document.getElementByID(). What ID is it going to grab if there are multiple ones?
On a slightly related topic, you can add multiple classes to a DIV. See Eric Myers discussion at,
Not sure why Ross has been downvoted there.
You can only have one ID per element, but you can indeed have more than one class. But don't have multiple class attributes, put multiple class values into one attribute.
<div id="foo" class="bar baz bax">
is perfectly legal.
I know this is a year old but I was curious about this myself and I'm sure others will find their way here. The simple answer is no, as others have said before me. An element can't have more than one ID and an ID can't be used more than once in a page. Try it out and you'll see how well it doesn't work.
In reponse to tvanfosson's answer regarding the use of the same ID in two different elements. As far as I'm aware an ID can only be used once in a page regardless of whether it's attached to a different tag.
By definition, an element needing an ID should be unique but if you need two ID's then it's not really unique and needs a class instead.
I don´t think you can have two Id´s but it should be possible. Using the same id twice is a different case... like two people using the same passport. However one person could have multiple passports... Came looking for this since I have a situation where a single employee can have several functions. Say "sysadm" and "team coordinator" having the id="sysadm teamcoordinator" would let me reference them from other pages so that employees.html#sysadm and employees.html#teamcoordinator would lead to the same place... One day somebody else might take over the team coordinator function while the sysadm remains the sysadm... then I only have to change the ids on the employees.html page ... but like I said - it doesn´t work :(