基本语法
If you are embedding this in XML, you had better place the ending '?>' there or the XML parser will puke on you. XML parsers do not like processing instructions without end tags, regardless of what PHP does.
If you're doing HTML like 90% of the world, or if you are going to process/interpret the PHP before the XML parser ever sees it, then you can likely get away with it, but it's still not best practice for XML.
指令分隔符
同 C 或 Perl 一样，PHP 需要在每个语句后用分号结束指令。一段 PHP 代码中的结束标记隐含表示了一个分号；在一个 PHP 代码段中的最后一行可以不用分号结束。如果后面还有新行，则代码段的结束标记包含了行结束。
<?php
echo "This is a test";
?>
<?php echo "This is a test" ?>
<?php echo 'We omitted the last closing tag';
Note: 文件末尾的 PHP 代码段结束标记可以不要，有些情况下当使用 include() 或者 require() 时省略掉会更好些，这样不期望的白空格就不会出现在文件末尾，之后仍然可以输出响应标头。在使用输出缓冲时也很便利，就不会看到由包含文件生成的不期望的白空格。
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User Contributed Notes指令分隔符
james dot d dot noyes at lmco dot com
06-May-2008 02:42
06-May-2008 02:42
Krishna Srikanth
17-Aug-2006 07:44
17-Aug-2006 07:44
Do not mis interpret
<?php echo 'Ending tag excluded';
with
<?php echo 'Ending tag excluded';
<p>But html is still visible</p>
The second one would give error. Exclude ?> if you no more html to write after the code.