Question

Is data-theme or data-role belong to html5?
If it isn’t belong html how browser render it without knowing this attribute?
Can I add a new attribute to html document and say browser “render this like that” ?

Answer 1

This link is telling that:

data- attributes are a wonderful new feature of HTML5 that let you add
any attributes you like to an element. All you have to do is start
your attribute name with the data- prefix.