Created attachment 547 [details]
A GDML file for Nested assembly example.

an <assembly> nested inside another <assembly> is not working the way I expected. Specifically, the inner assembly is not rendered in the VRML output file. 

A suggested fix as show bellow (in G4GDMLReadStructure::PhysvolRead() ):

   374    if (pAssembly)   // Fill assembly structure
   375    {
   376      if(assembly)                                       //Add this
   377      pAssembly->AddPlacedAssembly(assembly,transform);  //code
   378      if (!logvol) { return; }
   379      pAssembly->AddPlacedVolume(logvol, transform);
   380    }

In geant4-10.04, I have verified that this method works. In geant4-10.05, it is also feasible, but it is possible to encounter another problem ( https://bugzilla-geant4.kek.jp/show_bug.cgi?id=2140) I reported.