Reference-manual: Clarify fallback dependency types [skip ci]
@@ -361,8 +361,11 @@ otherwise. This function supports the following keyword arguments:
dependency is not found in the system. The value is an array
`['subproj_name', 'subproj_dep']` where the first value is the name
of the subproject and the second is the variable name in that
- subproject that contains the value of
- [`declare_dependency`](#declare_dependency).
+ subproject that contains a dependency object such as the return
+ value of [`declare_dependency`](#declare_dependency) or
+ [`dependency()`](#dependency), etc. Note that this means the
+ fallback dependency may be a not-found dependency, in which
+ case the value of the `required:` kwarg will be obeyed.
- `language` *(added 0.42.0)* defines what language-specific
dependency to find if it's available for multiple languages.
- `method` defines the way the dependency is detected, the default is
