You should always use
<?php ?> tags or short-echo tags
<?= ?>. Other variations (in particular, short tags
<? ?>) should not be used as they are commonly disabled by system administrators.
When a file is not expected to produce output (the entire file is PHP code) the closing
?> syntax should be omitted to avoid unintentional output, which can cause problems when a client parses the document, in particular some browsers fail to recognise the
<!DOCTYPE tag and activate Quirks Mode.
Example of a simple PHP script:
Example class definition file:
Example of PHP embedded in HTML: