Some apparently public header files include private header files. This usually means that these public header files should have been made private. And indeed most of them don't seem to define any part of the public Qt API.

$ grep _p.h src///*[^_]?.h
src/gui/embedded/qwssocket_qws.h:#include <QtGui/private/qunixsocketserver_p.h>
src/gui/embedded/qwssocket_qws.h:#include <QtGui/private/qunixsocket_p.h>
src/xmlpatterns/api/qxmlname.h: /* The implementation for these functions are in utils/qnamepool_p.h. */
$ grep _p.h src////[^_]?.h
src/plugins/gfxdrivers/directfb/qdirectfbpaintengine.h:#include <private/qpaintengine_raster_p.h>
src/plugins/gfxdrivers/directfb/qdirectfbpixmap.h:#include <QtGui/private/qpixmapdata_p.h>
src/plugins/gfxdrivers/directfb/qdirectfbsurface.h:#include <private/qpaintengine_raster_p.h>
src/plugins/gfxdrivers/directfb/qdirectfbsurface.h:#include <private/qwindowsurface_qws_p.h>
src/plugins/gfxdrivers/hybrid/hybridsurface.h:#include <private/qglwindowsurface_qws_p.h>
src/plugins/gfxdrivers/hybrid/hybridsurface.h:#include <private/qglpaintdevice_qws_p.h>
src/plugins/gfxdrivers/hybrid/hybridsurface.h:#include <private/qwssharedmemory_p.h>
src/sql/drivers/ibase/qsql_ibase.h:#include <QtSql/private/qsqlcachedresult_p.h>
src/sql/drivers/oci/qsql_oci.h:#include <QtSql/private/qsqlcachedresult_p.h>
src/sql/drivers/sqlite2/qsql_sqlite2.h:#include <QtSql/private/qsqlcachedresult_p.h>
src/sql/drivers/sqlite/qsql_sqlite.h:#include <QtSql/private/qsqlcachedresult_p.h>
src/sql/drivers/tds/qsql_tds.h:#include <QtSql/private/qsqlcachedresult_p.h>
$