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

Readability, a lot of HTML is not coded by people with computer science backgrounds so the concept of "Boolean" would be foreign to them in those terms. Also it improves readability for Computer Science and other technical users by providing reinforced clues as to the function of a given statement.