titleFn(attr, ...args) {
		let s = null;

		if (typeof(this[attr]) == 'function')
			s = this[attr](...args);
		else if (typeof(this[attr]) == 'string')
			s = args.length ? this[attr].format(...args) : this[attr];

		if (s != null)
			s = this.stripTags(String(s)).trim();

		if (s == null || s == '')
			return null;

		return s;
	}
Format the given named property as title string.

This function looks up the given named property and formats its value
suitable for use as element caption or description string. It also
strips any HTML tags from the result.

If the property value is a string, it is passed to `String.format()`
along with any additional parameters passed to `titleFn()`.

If the property value is a function, it is invoked with any additional
`titleFn()` parameters as arguments and the obtained return value is
converted to a string.

In all other cases, `null` is returned.

@param {string} property
The name of the element property to use.

@param {...*} fmt_args
Extra values to format the title string with.

@returns {string|null}
The formatted title string or `null` if the property did not exist or
was neither a string nor a function.