[Javascript] Help finding information about script

[Peter Vogel]

I have found an example script on Microsoft's website which
I want to understand.  Where do I find definitions of things
like "document" properties, "external.menuArguments" etc.

Thank you

Peter

This is the script:
var win = external.menuArguments;
document.all.location.value = win.document.location.href;
document.all.location.select();
document.execCommand("Copy");