Q: Is it important what tags you put at the very top of your HTML code?

Dear Kalena...

Is it important what you put in TAGS at the very top? At the moment I'm using:

<< !doctype html public "-//W3C//DTD HTML 4.0 Transitional//EN" >>
html
head
etc…….

I've just seen this code and I'm wondering what it is:

<< ?xml version="1.0" encoding="iso-8859-1"? >>
http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd" >>
<< xmlns="http://www.w3.org/1999/xhtml >>

[all code deliberately broken for viewing purposes]

Regards
Ros