HTML sanitization
Encyclopedia
HTML sanitization is the process of examining an HTML document and producing a new HTML document that preserves only whatever tags are designated "safe". HTML sanitization can be used to protect against cross-site scripting
Cross-site scripting
Cross-site scripting is a type of computer security vulnerability typically found in Web applications that enables attackers to inject client-side script into Web pages viewed by other users. A cross-site scripting vulnerability may be used by attackers to bypass access controls such as the same...

 and SQL injection
SQL injection
A SQL injection is often used to attack the security of a website by inputting SQL statements in a web form to get a badly designed website in order to dump the database content to the attacker. SQL injection is a code injection technique that exploits a security vulnerability in a website's software...

 attacks by sanitizing any HTML code submitted by a user.

Tags often allowed are , , , , and .

In PHP
PHP
PHP is a general-purpose server-side scripting language originally designed for web development to produce dynamic web pages. For this purpose, PHP code is embedded into the HTML source document and interpreted by a web server with a PHP processor module, which generates the web page document...

this can be performed using the strip_tags function.
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