It's not a lot more than curiosity,
which is the difference between <br> and <br /> ?

I see both of them widely used and abused, are they completely interchangeable ?

This <br> tag is best used in HTML format using( .html extension ) and this <br /> tag goes with XHTML (or .xhtml saved document ).

It's not a lot more than curiosity,
which is the difference between <br> and <br /> ?

I see both of them widely used and abused, are they completely interchangeable ?

<br/> is used in XHTML which is a much stricter form of html :) .

So in any case there are no cons using <br/> instead of <br> even in "simple" HTML ?
<br/> is the same withot space btw 'r' and '/' ?

<br/> <!-- or --> <br /> it doesn't matter as long as you are using it with the correct doctype.

<br/> <!-- or --> <br /> it doesn't matter as long as you are using it with the correct doctype.

I don't get it, can you please show me with an example the relation to the doctype?

The space is there in <br /> to make the self-closing tags compatible with IE 6 and earlier. IE renders it wrong without the space.

the main difference between <br > and <br /> is <br> is used html earlier versions and <br /> is used in the latest version like the below tags also

<img src="" > ------------- <img src=""  />
<b> </b>---------------- <strong> </strong>
<i> -------------- <em> </em>

Ok, so it's definitely better to use <br /> in any case from my pov...