Sometimes, you may encounter problem with old PHP code where short open tags are used.
To enable short tags enable the setting called short_open_tag in the php.ini file.
However, short open tags will be removed in PHP 6.
Therefore, I do not recommend you to use short tags.
You should use the full length tags.
The php.ini short_open_tag directive determines whether or not PHP will recognize code between tags as PHP source which should be processed as such.
It’s been recommended for several years that you not use the short tag “short cut” and instead use the full tag combination.
With the wide spread use of XML and use of these tags by other languages, the server can become easily confused and end up parsing the wrong code in the wrong context.
But because this short cut has been a feature for such a long time, it’s currently still supported for backwards compatibility, but I will recommend you don’t use them.
Asoke Mukherjee's Blog 