/**
	 * Get tag by spec name.
	 *
	 * @since 1.5
	 *
	 * @param string $spec_name Spec name.
	 * @return array|null Allowed tag spec, or null if the tag does not exist.
	 */
	public static function find_tag_spec( $spec_name ) {
		foreach ( self::$allowed_tags as $tag_name => $allowed_tag ) {
			foreach ( $allowed_tag as $rule_spec ) {
				if (
					( ! isset( $rule_spec['tag_spec']['spec_name'] ) && $tag_name === $spec_name )
					||
					( isset( $rule_spec['tag_spec']['spec_name'] ) && $rule_spec['tag_spec']['spec_name'] === $spec_name )
				) {
					return array_merge( compact( 'tag_name' ), $rule_spec );
				}
			}
		}
		return null;
	}