function guessFontAvailability (desiredFont) {
	// create an element with the desired font family
	var a = document.createElement ('span');
	a.appendChild (document.createTextNode ('AAA'));
	a.style.fontFamily = desiredFont + ', monospace';
	a.style.fontSize = '100px';
	a.style.visibility = 'hidden';
	// create an element which will use the browser's default monospace font
	var b = document.createElement ('span');
	b.appendChild (document.createTextNode ('AAA'));
	b.style.fontFamily = 'monospace';
	b.style.fontSize = '100px';
	b.style.visibility = 'hidden';
	// attach the elements to the body
	document.body.appendChild (a);
	document.body.appendChild (b);
	// check if the dimensions of the elements are similar
	var available = true;
	if (a.offsetWidth === b.offsetWidth &&
		a.offsetHeight === b.offsetHeight) {
		available = false;
	}
	// remove the elements and return the availability of the font
	a.parentNode.removeChild (a);
	b.parentNode.removeChild (b);
	return available;
}