protected function validate_fields( $posted_data, $location, $fields, $action ) {

		/**
		 * Run an action immediately prior to user registration or update.
		 *
		 * The dynamic portion of this hook, `$action`, can be either "registration" or "update".
		 *
		 * @since 3.0.0
		 * @since 5.0.0 Moved from `LLMS_Person_Handler::update()` & LLMS_Person_Handler::register().
		 *              Added parameters `$fields` and `$args`.
		 *              Triggered by `do_action_ref_array()` instead of `do_action()` allowing modification
		 *              of `$posted_data` and `$fields` via hooks.
		 *
		 * @param array   $posted_data Array of user-submitted data (passed by reference).
		 * @param string  $location    Form location.
		 * @param array[] $fields      Array of LifterLMS Form Fields (passed by reference).
		 */
		do_action_ref_array( "lifterlms_before_user_{$action}", array( &$posted_data, $location, &$fields ) );

		// Check for all required fields.
		$required = $this->validator->validate_required_fields( $posted_data, $fields );

		/**
		 * Filter the required fields validity of the form submission.
		 *
		 * The dynamic portion of this hook, `$action`, can be either "registration" or "update".
		 *
		 * @since 5.0.1
		 *
		 * @param WP_Error|true $valid       Error object containing required validation errors or true when the data is valid.
		 * @param array         $posted_data Array of user-submitted data.
		 * @param string        $location    Form location.
		 */
		$required = apply_filters( "lifterlms_user_{$action}_required_data", $required, $posted_data, $location );

		if ( is_wp_error( $required ) ) {
			return $this->submit_error( $required, $posted_data, $action );
		}

		$posted_data = wp_unslash( $posted_data );

		$valid = $this->validator->validate_fields( $posted_data, $fields );
		if ( is_wp_error( $valid ) ) {
			return $this->submit_error( $valid, $posted_data, $action );
		}

		// Validate matching fields.
		$matches = $this->validator->validate_matching_fields( $posted_data, $fields );
		if ( is_wp_error( $matches ) ) {
			return $this->submit_error( $matches, $posted_data, $action );
		}

		/**
		 * Filter the validity of the form submission.
		 *
		 * The dynamic portion of this hook, `$action`, can be either "registration" or "update".
		 *
		 * @since 3.0.0
		 * @since 5.0.0 Unknown.
		 *
		 * @param WP_Error|true $valid       Error object containing validation errors or true when the data is valid.
		 * @param array         $posted_data Array of user-submitted data.
		 * @param string        $location    Form location.
		 */
		$valid = apply_filters( "lifterlms_user_{$action}_data", true, $posted_data, $location );
		if ( is_wp_error( $valid ) ) {
			return $this->submit_error( $valid, $posted_data, $action );
		}

		/**
		 * Run an action immediately after user registration/update fields have been validated.
		 *
		 * The dynamic portion of this hook, `$action`, can be either "registration" or "update".
		 *
		 * @since 3.0.0
		 * @since 5.0.0 Moved from `LLMS_Person_Handler::update()` & LLMS_Person_Handler::register().
		 *              Added parameters `$fields` and `$args`.
		 *
		 * @param array   $posted_data Array of user-submitted data.
		 * @param string  $location    Form location.
		 * @param array[] $fields      Array of LifterLMS Form Fields.
		 */
		do_action( "lifterlms_user_{$action}_after_validation", $posted_data, $location, $fields );

		return true;

	}