How do i know that i'm using a html5 editor or not ?

Question

making a html document, i used the tag <marquee >that isn't supported in html5 and really it didn't work. but another day my friend tried it in the same text editor and it worked.for me it is then a confusion.please help me.

Answer 1

You may consider to use the official validator below:-

https://validator.w3.org

It's important to know that there's nothing prevent the author to write something obsolete or nonsense in HTML as the browser will always try it best to parse and render it.

Most browser happily display obsolete elements as no user will happy to see a broken website and thus the responsibility still rely on us.

Answer 2

Here is how the obsolete <marquee> tag is used:

https://developer.mozilla.org/en-US/docs/Web/HTML/Element/marquee

Answer 3

thank