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_wp_specialchars() WP 1.2.2

Converts a number of special characters into their HTML entities.

Specifically deals with: &, <, >, ", and '.

$quote_style can be set to ENT_COMPAT to encode " to ", or ENT_QUOTES to do both. Default is ENT_NOQUOTES where no quotes are encoded.

This is an internal function for using it by WP core itself. It's not recommended to use this function in your code.

No Hooks.

Return

String. The encoded text with HTML entities.

Usage

_wp_specialchars( $string, $quote_style, $charset, $double_encode );
$string(string) (required)
The text which is to be encoded.
$quote_style(int|string)
Converts double quotes if set to ENT_COMPAT, both single and double if set to ENT_QUOTES or none if set to ENT_NOQUOTES. Converts single and double quotes, as well as converting HTML named entities (that are not also XML named entities) to their code points if set to ENT_XML1. Also compatible with old values; converting single quotes if set to 'single', double if set to 'double' or both if otherwise set.
Default: ENT_NOQUOTES
$charset(false|string)
The character encoding of the string.
Default: false
$double_encode(true|false)
Whether to encode existing HTML entities.
Default: false

Changelog

Since 1.2.2 Introduced.
Since 5.5.0 $quote_style also accepts ENT_XML1.

Code of _wp_specialchars() WP 5.7.2

<?php
function _wp_specialchars( $string, $quote_style = ENT_NOQUOTES, $charset = false, $double_encode = false ) {
	$string = (string) $string;

	if ( 0 === strlen( $string ) ) {
		return '';
	}

	// Don't bother if there are no specialchars - saves some processing.
	if ( ! preg_match( '/[&<>"\']/', $string ) ) {
		return $string;
	}

	// Account for the previous behaviour of the function when the $quote_style is not an accepted value.
	if ( empty( $quote_style ) ) {
		$quote_style = ENT_NOQUOTES;
	} elseif ( ENT_XML1 === $quote_style ) {
		$quote_style = ENT_QUOTES | ENT_XML1;
	} elseif ( ! in_array( $quote_style, array( ENT_NOQUOTES, ENT_COMPAT, ENT_QUOTES, 'single', 'double' ), true ) ) {
		$quote_style = ENT_QUOTES;
	}

	// Store the site charset as a static to avoid multiple calls to wp_load_alloptions().
	if ( ! $charset ) {
		static $_charset = null;
		if ( ! isset( $_charset ) ) {
			$alloptions = wp_load_alloptions();
			$_charset   = isset( $alloptions['blog_charset'] ) ? $alloptions['blog_charset'] : '';
		}
		$charset = $_charset;
	}

	if ( in_array( $charset, array( 'utf8', 'utf-8', 'UTF8' ), true ) ) {
		$charset = 'UTF-8';
	}

	$_quote_style = $quote_style;

	if ( 'double' === $quote_style ) {
		$quote_style  = ENT_COMPAT;
		$_quote_style = ENT_COMPAT;
	} elseif ( 'single' === $quote_style ) {
		$quote_style = ENT_NOQUOTES;
	}

	if ( ! $double_encode ) {
		// Guarantee every &entity; is valid, convert &garbage; into &amp;garbage;
		// This is required for PHP < 5.4.0 because ENT_HTML401 flag is unavailable.
		$string = wp_kses_normalize_entities( $string, ( $quote_style & ENT_XML1 ) ? 'xml' : 'html' );
	}

	$string = htmlspecialchars( $string, $quote_style, $charset, $double_encode );

	// Back-compat.
	if ( 'single' === $_quote_style ) {
		$string = str_replace( "'", '&#039;', $string );
	}

	return $string;
}