I'm considering writing code which produces an HTML tag that could have duplicate attributes, like this:
<div data-foo="bar" class="some-class" data-foo="baz">
Is this legal HTML? Does one of the data-foo
-values take precendence over the other? Can I count on semi-modern browsers (IE >= 9) to parse it without choking?
Or am I about to do something really stupid here?
The multiple attribute in HTML allows user to enter more than one value. It is a Boolean attribute and can be used on <input> as well as <select> element, To allow multiple file uploads in HTML forms, use the multiple attribute. The multiple attribute works with email and file input types.
Yes and no. It would be a single data attribute value, but you could split them into separate values with JavaScript.
A data attribute is a custom attribute that stores information. Data attributes always start with “data-” then followed with a descriptive name of the data that is being stored. You can have multiple data attributes on an element and be used on any HTML element.
It is not valid to have the same attribute name twice in an element. The authoritative references for this are somewhat complicated, as old HTML versions were nominally based on SGML and the restriction is implied by a normative reference to the SGML standard. In HTML5 PR, section 8.1.2.3 Attributes explicitly says: “There must never be two or more attributes on the same start tag whose names are an ASCII case-insensitive match for each other.”
What happens in practice is that the latter attribute is ignored. Well, future browsers might do otherwise. In the DOM, attributes appear as properties of the element node as well as in the attributes
object, so there would be no natural way to store two values.
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