Escaping from HTML

Everything outside 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. 

<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>

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 to skip over. 

<?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.