The Configuration object got a bit smarter in the later versions and it is not documented anywhere. Using GetValueOrDefault() should not be necessary anymore. When defining a new configuration field, using
Configuration.AddEditBox("z", "Z", "", 0.8);
should be perfectly fine and the last used value will be remembered. In the rare cases, where that is not the desired behavior, you can use an extra parameter at the end and set it to "true":
Configuration.AddEditBox("z", "Z", "", 0.8, true);
When reading the set values in the execution script, you can just type:
var z = Configuration.z;
That is only possible if the name of the parameter is a valid JavaScript identifier (does not have weird characters or spaces in it).
The JavaScript engine used in RW apps is the default engine that comes with Windows/Internet Explorer - having later versions of IE installed (even if you do not use it) may result in better speeds.