In last week's release some changes to patching with WiX were made with more exciting changes to come. Peter Marcu has implemented some changes he'll talk more about on his blog, but suffice to say has reduced the number of commands and command line arguments required to build a patch.

I've added some documentation for the new the patch build system in WiX v3 adapted from Peter's blog post, as well as updated the documentation for patch build using Patch Creation Properties and PatchWiz.dll.

Another very important change was defaulting the patch transform validation bits to 0x0922001f. This is crucial since the previous validation bits were merely 0x0002001f which means that only the ProductCode is checked. This means that the patch can apply to any ProductVersion and, therefore, small updates will always sequence after minor upgrades. This can lead to regressions including older registry values written to the registry and even older files written to disk. If you plan on shipping patches produced with WiX v3 using the new patch system you should pick up the latest drop. In the near future these validation bits will be configurable in WiX.