HTML - Why boolean attributes do not have boolean value?

Question

I noticed that some elements have attributes which are boolean. I wonder why the values are not true or false? or 1 and 0? Are there any reason behind why they are like this

Answer 1

As vc74 has said, it doesn't matter what value you have for selected or disabled.

<option selected="selected">Ham Burger</option>

will do the same as

<option selected="sjkhdaskj">Ham Burger</option>