Rollback custom actions

Custom actions that are scheduled as "deferred" execute during the Execute sequence's rollback-protected phase. To give those actions rollback capabilities, you'll need to author separate custom actions that undo the work. These are scheduled as "rollback" . Rollback custom actions are scheduled before the action they're meant to revert in case of an error. Here's an example:

<CustomAction Id="systemChangingCA" Execute="deferred" 
Script="vbscript">
      msgbox "Imagine this changes the system in some way"
</CustomAction>

<CustomAction Id="myRollbackCA" Execute="rollback" 
Script="vbscript">
      msgbox "Imagine this undoes the changes"
</CustomAction>

<CustomAction Id="causeError" Execute="deferred" 
   Script="vbscript">
      return failure
</CustomAction>

We'll schedule these during the Execute sequence.

<InstallExecuteSequence>
   <Custom Action="myRollbackCA" Before="systemChangingCA" />
   <Custom Action=...