PackageGroups

To split your package definitions up for more modularity, place them within PackageGroup elements. You can then reference the group within your Chain element with PackageGroupRef. The following is an example where we separate the detection (via RegistrySearch) and installation of SQL Server into its own fragment:

<Bundle Name="Awesome Software Bundle"
        Version="1.0.0.0" 
        Manufacturer="Awesome Company"
        Copyright="(c) All rights reserved."
        UpgradeCode="3601032C-A8C9-4323-88E0-1967A9C2145E">

   <BootstrapperApplicationRef  
      Id="WixStandardBootstrapperApplication.RtfLicense" />

      <Chain>
         <PackageGroupRef Id="SQL_SERVER_2012_EXPRESS"/>
      </Chain>
</Bundle>

<Fragment>
   <util:RegistrySearch
      Id="SqlInstanceFound"
      Root="HKLM" 
      Key="SOFTWARE\Microsoft\Microsoft SQL Server\Instance Names\SQL" 
      Value="$(var.SqlServerInstance)"
      Result="exists" 
      Variable...