<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>
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.
Advanced escaping using conditions
<?php if ($expression == true): ?>
This will show if the expression is true.
<?php else: ?>
Otherwise this will show.
<?php endif; ?>
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 that is not met.