What are “data-url” and “data-key” attributes of tag?

Question

I\'ve faced two strange attributes of an html tag . They are \"data-url\" and \"data-key\".

What are they and how

Answer 1

data-* attributes are for adding arbitrary data to an element for use solely by the code (usually client side JavaScript) running on the site hosting the HTML.

In order to tell what the three examples you give are for, we would have to reverse engineer the code that comes with them (unless they are documented on the sites) since they don't have standard meanings.