Delimiters

The PHP processor only parses code within its delimiters (the trigger symbols). Anything outside its delimiters is sent directly to the output and not parsed by PHP. The most common open/close delimiters are "<?php" and "?>" so that a section of PHP markup appears within the set of angle-brackets "<?php.....?>" (see examples below in boxes). Other delimiters, in the form "<script language="php">" and "</script>", are also always available, so these two forms are the most portable. The first form of delimiters, <?php and ?>, in XHTML and other XML documents, creates correctly formed XML processing instructions.[1] Therefore, in either of these two cases, the resulting mixture of PHP and other markup is well-formed, and so probably valid, as XML and XHTML on the server before PHP processing. This may be helpful if the source code documents ever need to be processed in other ways during the life of the software.

Short opening tags (<? or <?=) are also available for use, but are, along with ASP style tags (<% or <%=), less-portable, as they can be disabled in the PHP configuration. For this reason, the use of Short tags and ASP style tags is discouraged.[2] The purpose of these delimiters is to separate PHP code from non-PHP code (notably HTML). Everything outside the delimiters is ignored by the PHP parser and is passed through as output.[3]