ing.
		The default value for this field is function <code>debug.getupvalue</code> of the Lua debug library if it is loaded at the moment this class is required.
	</dd>
	
	<dt><code><b>userdata</b></code></dt>
	<dd>
		Field that defines the method implementation used to compare two different userdata values passed as parameters.
		The function must return <code>true</code> if the values match or <code>false</code> otherwise.
		If this field evaluates to <code>false</code> then userdata values are compared fo