凡是在一对开始和结束标记之外的内容都会被 PHP 解析器忽略，这使得 PHP 文件可以具备混合内容。 可以使 PHP 嵌入到 HTML 文档中去，如下例所示。
<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>
使用条件结构：
Example #1 使用条件的高级分离术
<?php if ($expression == true): ?>
This will show if the expression is true.
<?php else: ?>
Otherwise this will show.
<?php endif; ?>
要输出大段文本时，跳出 PHP 解析模式通常比将文本通过 echo 或 print 输出更有效率。
Note:
此外注意如果将 PHP 嵌入到 XML 或 XHTML 中则需要使用
<?php ?>标记以保持符合标准。
Since it's not documented (AFAICT) and it might cause confusion: a single line break immediately after ?> is ignored. Since whitespace is hard to see, whitespace is replaced with _ and the following code
<?php echo '1'; ?>
<?php echo '2'; ?>_
<?php echo '3'; ?>
_<?php echo '4'; ?>_<?php echo '5'; ?>
will produce
12_
3_4_5
<p>This is ignore by the php parser and displayed by the browser </p>
<?php echo "While this is going to be parsed"; ?>
<?php
when php interpreter hits the closing tag it start to outputing everything whatever it finds until it hit another opening tag.If php interpreter find a conditional statement in the middle of a block then php interpreter decided which block skip
Advanced escaping using conditions
<?php $a = 10; if($a<100): ?>
This conditional block is executed
<?php else: ?>
otherwise this will be executed
<?php endif; ?>
In php 5 version,there are 5 opening and closing tags.
1.<?php echo "standard long form php tag and if you use xml with php this tag will be use";?>
2.<?= "short echo tag and alwayes available from 5.4.0";?>
3.<? echo "short open tag which is available if short_open_tag is enable in php ini configuration file directive or php was configured with --enable-short-tags.This tag has discoursed from php 7.If you want to use xml with php,then short_open_tag in php ini will be disabled";?>
4.<script language="php">
echo "Some editor do not like processing the code within this tag and this tag is removed from php 7.0.0 version";
</script>
5.<% echo "asp style tag and asp_tags should be enabled but now php 7.0.0 version,this tag is removed";%>
When the PHP interpreter hits the ?> closing tags, it WON'T output right away if it's inside of a conditional statement:
(no matter if it's an Alternative Syntax or not)
<html>
<?php
$a = 1;
$b = 2;
if ($a === 1) {
if ($b == 2) {
?><head></head><?php
} else {
?><body></body><?php
}
}
?>
</html>
This would output `<html><head></head></html>`.
Aside from conditional statements, the PHP interpreter also skip over functions! What a surprise!
<html>
<?php
function show($a) {
?>
<a href="https://www.<?php echo $a ?>.com">
Link
</a>
<?php
}
?>
<body>
<?php show("google") ?>
</body>
</html>
This gives `<html><body><a href="https://www.google.com">Link</a></body></html>`.
These really confused me, because at first I thought it would output any HTML code right away, except for Alternative Syntaxes (https://www.php.net/manual/en/control-structures.alternative-syntax.php). There are more strange cases than I thought.
Version of 7.0.0,3 tags are available in php.
1.long form tag (<?php ?>)
2.short echo tag(<?= ?>)
3.short_open_tag(? ?)
You can use short_open_tag when you start xml with php.
"<script language="php"> </script>, are always available." since PHP 7.0.0 is no longer true. These are removed along the ASP "<%, %>, <%=" tags.
Although not specifically pointed out in the main text, escaping from HTML also applies to other control statements:
<?php for ($i = 0; $i < 5; ++$i): ?>
Hello, there!
<?php endfor; ?>
When the above code snippet is executed we get the following output:
Hello, there!
Hello, there!
Hello, there!
Hello, there!
It's possible to write code to create php escapes which can be processed later by substituting \x3f for '?' - as in echo "<\x3fphp echo 'foo'; \x3f>";
This is useful for creating a template parser which later is rendered by PHP.
When the documentation says that the PHP parser ignores everything outside the <?php ... ?> tags, it means literally EVERYTHING. Including things you normally wouldn't consider "valid", such as the following:
<html><body>
<p<?php if ($highlight): ?> class="highlight"<?php endif;?>>This is a paragraph.</p>
</body></html>
Notice how the PHP code is embedded in the middle of an HTML opening tag. The PHP parser doesn't care that it's in the middle of an opening tag, and doesn't require that it be closed. It also doesn't care that after the closing ?> tag is the end of the HTML opening tag. So, if $highlight is true, then the output will be:
<html><body>
<p class="highlight">This is a paragraph.</p>
</body></html>
Otherwise, it will be:
<html><body>
<p>This is a paragraph.</p>
</body></html>
Using this method, you can have HTML tags with optional attributes, depending on some PHP condition. Extremely flexible and useful!
Playing around with different open and close tags I discovered you can actually mix different style open/close tags
some examples
<%
//your php code here
?>
or
<script language="php">
//php code here
%>
One aspect of PHP that you need to be careful of, is that ?> will drop you out of PHP code and into HTML even if it appears inside a // comment. (This does not apply to /* */ comments.) This can lead to unexpected results. For example, take this line:
<?php
$file_contents = '<?php die(); ?>' . "\n";
?>
If you try to remove it by turning it into a comment, you get this:
<?php
// $file_contents = '<?php die(); ?>' . "\n";
?>
Which results in ' . "\n"; (and whatever is in the lines following it) to be output to your HTML page.
The cure is to either comment it out using /* */ tags, or re-write the line as:
<?php
$file_contents = '<' . '?php die(); ?' . '>' . "\n";
?>
These methods are just messy. Short-opening tags and ASP-styled tags are not always enabled on servers. The <script language="php"></script> alternative is just out there. You should just use the traditional tag opening:
<?php?>
Coding islands, for example:
<?php
$me = 'Pyornide';
?>
<?=$me;?> is happy.
<?php
$me = strtoupper($me);
?>
<?=$me;?> is happier.
Lead to something along the lines of messy code. Writing your application like this can just prove to be more of an
inconvenience when it comes to maintenance.
If you have to deal chunks of HTML, then consider having a templating system do the job for you. It is a poor idea to rely on the coding islands method as a template system in any way, and for reasons listed above.