From TheWarWiki

There's "optional dependencies" field in the .mod file, inside the <UiMod /> tag:

		<Dependencies>
			<Dependency name="RandomModName" optional="true" forceEnable="true" />
		</Dependencies>

The "optional" tag specifies whether the dependency must be present in order for this addon to load. If the specified mod isn't present, this dependency will be ignored; if it is present, it will be loaded before the current addon.

The "forceEnable" tag specifies whether or not the dependency should be automatically enabled if it is found to exist in the Interface\Addons path - if this is true, even if the dependency was explicitly turned off, it will be enabled by the client automatically and loaded before the current addon. If it's false, then it will not be. Note: This defaults to true. For optional dependencies, you should probably set this explicitly to false.