Please document that ProductSearch cannot be used to search for Bundles

[wixbot]

It is easy to get the impression that ProductSearch within a bundle can be used to detect previous versions of the same bundle - an upgrade code is specified in the Bundle element and ProductSearch allows you to search for products with a specific upgrade code.

In the answer to my question on StackOverflow (http://stackoverflow.com/q/33474944/227322), Bob explained that the ProductSearch only searches for msi packages, not bundles. It would be good if this was documented.

Originally opened by villintehaspam

[MarioVolarevic]

Also, what is with this issue (implement BundleSearch since ProductSearch doesn't work): #4550
I see that it is closed and milestone is 3.9, but I'm using 3.11 and there is no such feature.