UPDATE: Apache was not sending the php code to the engine because I had a typo in the upper php delimiter. I left the "<" out. I wrote "?php"
My php engine has been working just fine for a while. It is not working right now. Php code is sent back to the browser unparsed. I used yum to install everything originally. I haven't installed anything recently. As far as I can tell, nothing about the server (which is on a laptop on a private network behind a router) has changed.
This line in /etc/httpd/conf/httpd.conf is uncommented, just like it was when the php engine was working:
LoadModule php5_module modules/libphp5.so
I have very little practice diagnosing php engine issues. Can someone give me some ideas of how to start diagnosing this?