PHP5 and its backward compatibility

[marcnyc]

Hello, I am in the process of looking for a new hosting company.
I found one I like that has only PHP5. They say it is backward compatible, but I was wondering how true that is. I remember having installed some scripts on PHP5 once and I was getting a lot of errors that I didn't get in PHP4. This was a long time ago so I don't know how it is now.
I was wondering if somebody can tell me more about this and about how really backward compatible it is.

Thank you.

PS Some of the scripts I currently use are Simple Machine Forums, Mambo CMS, CopperMine Photo Gallery etc...

[thorpe]

This section of the manual might help you out.

[kwmccabe]

If you are using xml/xsl this is also helpful:
http://www.zend.com/php5/articles/php5-xmlphp.php

[MarkR]

Clearly, before you migrate, you should test all your applications thorougly on PHP5 on a local development server.

This server should have as close to an identical configuration to your production server as it is possible to make it. Ideally it should run the same PHP binary.

Mark