his->escape_function = $escape_function;

		// replace strings like this: {tagname attr="value"}
		$string = preg_replace_callback( '/\{(\w+)(\ +(?:(?!\{)[^}\n])+)*\}/', array( $this, 'replace_tag' ), $string );

		// call again to take care of nested variables
		$string = preg_replace_callback( '/\{(\w+)(\ +(?:(?!\{)[^}\n])+)*\}/', array( $this, 'replace_tag' ), $string );
		return $string;
	}

	/**
	 * @param string $string
	 *
	 * @return string
	 */
	protected function replace_in_html( $string ) {
		return $this->replace( $string, 'esc_html' );
	}

	/**
	 * @param string $string
	 *
	 * @return string
	 */
	protected function replace_in_attributes( $string ) {
		return $this->replace( $string, 'esc_attr' );
	}

	/**
	 * @param string $string
	 *
	 * @return string
	 */
	protected function replace_in_url( $string ) {
		return $this->replace( $string, 'urlencode' );
	}

	/**
	 * Gets data variable from cookie.
	 *
	 * @param array $args
	 *
	 * @return string
	 */
	protected function get_cookie( $args = array() ) {
		if ( empty( $args['name'] ) ) {
			return '';
		}

		$name    = $args['name'];
		$default = isset( $args['default'] ) ? $args['default'] : '';

		if ( isset( $_COOKIE[ $name ] ) ) {
			return esc_html( stripslashes( $_COOKIE[ $name ] ) );
		}

		return $default;
	}

	/*
	 * Get property of currently logged-in user
	 *
	 * @param array $args
	 *
	 * @return string
	 */
	protected function get_user_property( $args = array() ) {
		$property = empty( $args['property'] ) ? 'user_email' : $args['property'];
		$default  = isset( $args['default'] ) ? $args['default'] : '';
		$user     = wp_get_current_user();

		if ( $user instanceof WP_User && isset( $user->{$property} ) ) {
			return esc_html( $user->{$property} );
		}

		return $default;
	}

	/*
	 * Get property of viewed post
	 *
	 * @param array $args
	 *
	 * @return string
	 */
	protected function get_post_property( $args = array() ) {
		global $post;
		$property = empty( $args['property'] ) ? 'ID' : $args['property'];
		$default  = isset( $args['default'] ) ? $args['default'] : '';

		if ( $post instanceof WP_Post && isset( $post->{$property} ) ) {
			return $post->{$property};
		}

		return $default;
	}

	/**
	 * @return string
	 */
	protected function get_email() {
		if ( ! empty( $_REQUEST['EMAIL'] ) ) {
			return $_REQUEST['EMAIL'];
		}

		// then , try logged-in user
		if ( is_user_logged_in() ) {
			$user = wp_get_current_user();
			return $user->user_email;
		}

		// TODO: Read from cookie? Or add $_COOKIE support to {data} tag?
		return '';
	}

}