PHP regular expression method to verify basic HTML tags

PHP is an efficient web development language that supports regular expression functions and can quickly verify the validity of input data. In web development, HTML is a common markup language, and validating HTML tags is a very important method for web form validation. This article will introduce basic HTML tag verification methods and how to use PHP regular expressions for verification.

1. Basic structure of HTML tags

HTML tags consist of element names and attributes surrounded by angle brackets. Common tags include p, a, div, span, h1, img, etc. For example, the basic structure of the p tag is:

Example paragraph.

where p is the tag name and class is the attribute name , example is the attribute value, and Example paragraph is the label content.

2. Basic HTML tag verification method

HTML tag verification is usually performed using regular expressions. Regular expressions are codes that describe specific patterns of strings and can be applied in PHP. The following is the basic HTML tag validation method.

1. Verify open tags or self-closing tags

The regular expression to verify open tags or self-closing tags is:

/1>|1/>/ i

This regular expression can match all legal open tags and self-closing tags, where [a-z] indicates that the tag name consists of one or more lowercase letters, and is a word boundary, ¹* indicates other attributes, i indicates case insensitivity.

2. Verify the closing tag

The regular expression to verify the closing tag is:

/([a-z] )>/i

This regular expression can match all legal closing tags, where is the escape character and i means case insensitivity.

3. Verify no-content tag

The regular expression to verify no-content tag is:

/ 1*/>/i

This regular expression can match all legal content-less tags, where [a-z] is the tag name, is the word boundary, ¹* represents other attributes, /> represents a self-closing tag, and i represents case insensitivity.

3. Use PHP regular expressions to verify HTML tags

Basic HTML tag verification methods can be verified using the preg_match() function in PHP. The following is sample code to validate HTML tags:

$str = '

Example paragraph.

';
$ tagPattern = '/1>|1/>/i';
$endPattern = '/([a-z] )>/i';
$nonPattern = '/1*/>/i';

if (preg_match($tagPattern, $str)) {

echo "Opening tag detected.

";
}

if (preg_match($endPattern, $str)) {

echo "Closing tag detected.

";
}

if (preg_match($nonPattern, $str)) {

echo "Self-closing tag detected.

";
}
?>

In the above code, $str represents the verified HTML tag string, and $tagPattern represents the opening tag or self-closing tag Regular expression, $endPattern represents the regular expression of closed tags, $nonPattern represents the regular expression of no content tags. Use the preg_match() function to verify the HTML tag string from the standard input, the output result is:

Opening tag detected.
Closing tag detected.

4. Summary

Through the introduction of this article, we understand the basic HTML tag verification method and how to use PHP regular expressions for verification , to ensure the validity of the input data. In practical applications, we can also combine other verification methods, such as filtering illegal characters, verifying data types, etc., to ensure the security and reliability of web forms.

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