When PHP parses a file, it looks for opening and closing tags,
which are <?php and ?>
which tell PHP to start and stop interpreting the code between
them. Parsing in this manner allows PHP to be embedded in all
sorts of different documents, as everything outside of a pair
of opening and closing tags is ignored by the PHP parser.
PHP also allows for short open tags <? and ?>
(which are discouraged because they are only available if enabled with
file directive, or if PHP was configured with the --enable-short-tags
If a file is pure PHP code, it is preferable to omit the PHP closing tag at the
end of the file. This prevents accidental whitespace or new lines being added after the PHP
closing tag, which may cause unwanted effects because PHP will start output
buffering when there is no intention from the programmer to send any output
at that point in the script.