title: Remove InstallShield prerequisites if installation cancelled
body: <p>We use InstallShield 2010 to install our software using the InstallScript approach.  There are some prerequisites that may be installed as necessary.  In the <code>OnBegin</code> callback, we execute some logic to validate the system before continuing with the installation.  If the user cancels the installer at this point, the installation will exit, but the prerequisites are not uninstalled.  I have a few questions.</p>
  
  <p>1)  Is it possible to perform our custom validation before the prerequisites are ever installed?  This doesn't appear possible within InstallShield 2010 based on everything I've read, but I'd like to have that confirmed.</p>
  
  <p>2)  Is there a way to force the prerequisites to be uninstalled if the user cancels the installation?</p>
  
  <p>3)  Are there alternatives that would allow the prerequisites to be installed after the <code>OnBegin</code> callback?  I read something about prerequisites being tied to a particular feature, but it is unclear how to do this in the UI.</p>