Why should we use <?php for embedding php code?

I once posted a question here with php code embedded using <?. Someone told me I should NOT do that and I should use <?php

The person did not tell me why it is so. Can someone please explain why it is unsafe to us开发者_如何学Pythone <??

<? (the short tags) can be disabled in the PHP configuration, see short_open_tag.

• http://php.net/manual/en/ini.core.php

Why disable it? In some cases you'd want to use <?xml.. definitions for example, sure there are other ways to output that, but it's just safest to use <?php - especially if you plan on moving your code from server to server.