[da-x]

Specifications are important.

The better the specs of a commercial product, the easier it would be to produce an open source version it, with coding and testing automation perhaps even a one-to-one offering.

[hard_times]

well, you've got endless "integration testing" in the form of 3rd party software for Windows.

More reliable than any specification, considering Windows itself is a patchwork of workarounds to not break backward-compatibility.