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Escaping from HTML
Everything outside of a pair of opening and closing tags is ignored by the PHP parser which allows PHP files to have mixed content. This allows PHP to be embedded in HTML documents, for example to create templates.
Code:
<p>This is going to be ignored by PHP and displayed by the browser.</p>
<?php echo 'While this is going to be parsed.'; ?>
<p>This will also be ignored by PHP and displayed by the browser.</p>
This works as expected, because when the PHP interpreter hits the ?> closing tags, it simply starts outputting whatever it finds until it hits another opening tag unless in the middle of a conditional statement in which case the interpreter will determine the outcome of the conditional before making a decision of what which to skip over. See the next example.
Using structures with conditions
Example #1 Advanced escaping using conditions
Code:
<?php if ($expression == true): ?>
This will show if the expression is true.
<?php else: ?>
Otherwise this will show.
<?php endif; ?>
In this example PHP will skip the blocks where the condition is not met, even though they are outside of the PHP open/close tags, PHP skips them according to the condition since the PHP interpreter will jump over blocks contained within a condition what is not met.
For outputting large blocks of text, dropping out of PHP parsing mode is generally more efficient than sending all of the text through echo or print.
There are four different pairs of opening and closing tags which can be used in PHP. Two of those, <?php ?> and <script language="php"> </script>, are always available. The other two are short tags and ASP style tags, and can be turned on and off from the php.ini configuration file. As such, while some people find short tags and ASP style tags convenient, they are less portable, and generally not recommended.
Example #2 PHP Opening and Closing Tags
Code:
1. <?php echo 'if you want to serve XHTML or XML documents, do it like this'; ?>
2. <script language="php">
echo 'some editors (like FrontPage) don\'t
like processing instructions';
</script>
3. <? echo 'this is the simplest, an SGML processing instruction'; ?>
<?= expression ?> This is a shortcut for "<? echo expression ?>"
4. <% echo 'You may optionally use ASP-style tags'; %>
<%= $variable; # This is a shortcut for "<% echo . . ." %>
While the tags seen in examples one and two are both always available, example one is the most commonly used, and recommended, of the two.
Short tags are only available when they are enabled via the short_open_tag php.ini configuration file directive, or if PHP was configured with the --enable-short-tags option.
ASP style tags are only available when they are enabled via the asp_tags php.ini configuration file directive.
