[WordPress] Using wp_kses for custom data validation in WordPress.

00-building-a-custom-select-element.php

<?php

/**
 * For this example, we're not worried with i18n nor the function calls needed
 * to set variables like $pages. Assume that the pages are pulled earlier in the
 * lifecycle of the program.
 * 
 * There are other places in which you may want to validate information, but the purposes of
 * this example is ultimately to highlight how to customize the allowed HTML via wp_kses.
 */

$html = '<select>';
$html .= '<option>Select a page...</option>';

foreach ( $pages as $page ) {
  
	$html .= '<option>';
		$html .= $page->post_title;
	$html .= '</option>';

}

$html .= '</select>';

01-customizing-allowed-html.php

<?php

/**
 * We're going to allow the select element to have a name attribute
 * and allow the option elements to have both a value and selected
 * attribute.
 */

$allowed_html = array(
	'select' => array(
		'name' => array(),
	),
	'option' => array(
		'value'    => array(),
		'selected' => array(),
	),
);

02-custom-data-validation-with-wp-kses.php

<?php


$html = '<select name="acme[page]">';
$html .= '<option value="default">Select a page...</option>';

foreach ( $pages as $page ) {

	/** 
	 * Set a $selected variable here using a custom function or using
	 * WordPress' selected() helper.
	 */

	$html .= '<option value="' . $page->ID . '"' . $selected . '>';
		$html .= $page->post_title;
	$html .= '</option>';

}

$html .= '</select>';

$allowed_html = array(
	'select' => array(
		'name' => array(),
	),
	'option' => array(
		'value'    => array(),
		'selected' => array(),
	),
);

echo wp_kses( $html, $allowed_html );