Selecting a part of the scene (e.g., an Xform object) > right-click > export selected. This can be saved as .usd(a/c). Inspecting the file it can be seen that the path to textures is absolute - the usd file is not self-contained, and cannot be (i) shared with others, (ii) work if the texture is moved. Doing so raises many errors and warnings. Shouldn’t the usd file be self-containing and independent of external files?