Formatting: Add 'main' tag to kses

`main` is a valid HTML element that is especially valuable for KSES to support in light of full site editing.

Related: https://github.com/WordPress/gutenberg/pull/28576 for the addition of `main` to the group block.

Fixes #53156.
Props glendaviesnz.



git-svn-id: https://develop.svn.wordpress.org/trunk@50987 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/kses.php

@@ -252,6 +252,12 @@ if ( ! CUSTOM_TAGS ) {
 			'align' => true,
 			'value' => true,
 		),
+		'main'        => array(
+			'align'    => true,
+			'dir'      => true,
+			'lang'     => true,
+			'xml:lang' => true,
+		),
 		'map'        => array(
 			'name' => true,
 		),

tests/phpunit/tests/kses.php

@@ -1478,4 +1478,22 @@ EOF;
 
 		$this->assertSame( $html, wp_kses_post( $html ) );
 	}
+
+	/**
+	 * Test filtering a standard main tag.
+	 *
+	 * @ticket 53156
+	 */
+	function test_wp_kses_main_tag_standard_attributes() {
+		$test = array(
+			'<main',
+			'class="wp-group-block"',
+			'style="padding:10px"',
+			'/>',
+		);
+
+		$html = implode( ' ', $test );
+
+		$this->assertSame( $html, wp_kses_post( $html ) );
+	}
 }