HTML Versus XHTML (REPEATING COMPUTER SCIENCE, July 30, 2021)

I repeat "HTML Versus XHTML" (see W3SCHOOL, https://www.w3schools.com/html/html_xhtml.asp), when I forgot can I use <br> or <br />, and while it may be the same result, but here is explained the difference.

See also how define < and > (W3SCHOOL, https://www.w3schools.com/xml/xml_syntax.asp).