Found an weird Doxygen-ism today. Related to a doxygen list post , I found that if I had an `enum class` inside a namespace that was undocumented, I got this warning: Generating XML o/home/aron.helser/projects/cmb/smtk/src/smtk/io/mesh/MeshIO.h:31: warning: Internal inconsistency: member EntireResource does not belong to any container! The code that generated this error is from smtk . The outer namespaces are already documented. namespace smtk { namespace io { /// Mesh IO <<< adding this documentation fixed the warning. namespace mesh { /// Mesh subset types enum class Subset : unsigned int { EntireResource, OnlyDomain, OnlyDirichlet, OnlyNeumann, }; Hope that helps another confused Doxygen user.