Currently, QDoc includes all files from source/header directories that match a set file extension. It's possible to exclude files from the doc build with 'excludedirs' and 'excludefiles' - however, this doesn't easily allow exclusion of private header files (<filename>_p.h) located in the source directory along the public headers.
For most modules, this a not an issue; QDoc parses the private header files, finds no documentation for them, and therefore (correctly) assumes they are private/internal. But for Qt 3D this is a problem: It has a lot of private classes in public namespaces, and because a namespace is public, QDoc generates documentation for everything it sees in it, including private classes (and complains about missing documentation for them).
Therefore, QDoc needs a more flexible way to filter out source files, by using wildcards to match a filename pattern.