public function sanitize_email_type( $value ) {
		$value = trim( (string) $value );
		$new_value = '';

		if ( in_array( $value, [ 'html', 'text' ], true ) ) {
			$new_value = $value;
		}

		if ( ! $new_value ) {
			add_settings_error(
				'soter_email_type',
				'invalid_soter_email_type',
				sprintf(
					'Email type must be one of "text" or "html" - "%s" given.',
					esc_html( $value )
				)
			);

			return $this->email_type;
		}

		return $new_value;
	}