HTML supports data-* attribute type for custom attributes. You can read about it more here.
Definition and Usage The data-* attributes is used to store custom
data private to the page or application.The data-* attributes gives us the ability to embed custom data
attributes on all HTML elements.The stored (custom) data can then be used in the page’s JavaScript to
create a more engaging user experience (without any Ajax calls or
server-side database queries).The data-* attributes consist of two parts:
- The attribute name should not contain any uppercase letters, and must
be at least one character long after the prefix “data-”- The attribute value can be any string
Note: Custom attributes prefixed with “data-” will be completely ignored by the user agent.
Rather than just using size="A4" you can use data-size="A4"
Example
<div className="page" data-size="A4">
// ....
</div>