There are three kinds of tags to denote PHP blocks in a file. The PHP parser is looking for the opening and (if present) closing tags to delimit the code to interpret.
These tags are the standard method to embed PHP code in a file.
<?php echo "Hello World"; ?>
These tags are available in all PHP versions, and since PHP 5.4 are always enabled. In previous versions, echo tags could only be enabled in conjunction with short tags.
<?= "Hello World" ?>
You can disable or enable these tags with the option
<? echo "Hello World"; ?>
By enabling the
asp_tags option, ASP-style tags can be used.
<% echo "Hello World"; %>
These are an historic quirk and should never be used. They were removed in PHP 7.0.