Get a copy of Advanced Find and Replace, yeah it's $20 but I use it every day I code. Find "<?" and replace with "<?php" and it'll save you hours of time. While I suppose "<?" could be called shorthand it really doesn't apply to PHP like it does CSS.
The stricter your code the better and much more responsive you'll become. Turn up error-reporting to it's maximum setting in PHP...
...and make sure you address all errors including when variables aren't set and are referred to.
Create an .xhtml file on your desktop (from a Notepad template) and open it in Firefox: broken XML. You can code strict or loose, and strict might take a little longer to learn though you'll be so much more capable in the long term.