MSI Factory
This dialog contains a list of other merge modules that this merge module requires in order to install and operate properly. Although making entries here will not cause the other merge modules to be automatically included during a database merge, it will cause the build tool to catch the fact that the other modules are requested. If a dependent module is missing it causes a validation warning during the build of the main installer package.
Click the Add button to open the Merge Module Dependency Properties dialog and add a new dependency to this merge module.
MSDN Online: ModuleDependency Table
WiX Help File: Dependency Element