currently all my php generated rich html webpages start with this line, which I have been adding to my tempaltes YEARS ago... 

```html
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
    "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

```

UPDATE
======

**Who Should Use Which Doctype? When Should One Change Doctype?** When I remove this line all still works fine. Is it still essentially needed to put all that at the top of my pages? What are my alternatives? Thanks very much for your suggestions.