Using xverbs

Using

inkscape --xverbs=xverbs.yaml

Format of xverbs.yaml:

# only "verbose: yes" enable logging
verbose: yes

run:
  # open document to process
  - xverb-id: XFileOpen, gfx_sources/loading_screen/sandclock_atlas.svg

  # set label for XUndoToLabel "xverb" works
  # NB: if something wrong with undo labels use "verb" EditUndo instead of XUndoLabel and XUndoToLabel at all
  - xverb-id: XUndoLabel, fresh_document

  # select element to handle
  - xverb-id: XSelectElement, top_sand

  # usual "verbs"
  - verb-id: EditInvertInAllLayers
  - verb-id: EditDelete
  - verb-id: FitCanvasToDrawing

  # save element to separated svg document
  - xverb-id: XFileSaveAs, output/thegame/linux/data/gfx/loading_screen/top_sand.svg

  # also save png preview
  - xverb-id: XFileExportPNG, output/thegame/linux/data/gfx_preview/loading_screen/top_sand.png

  # return to the fresh_state of document
  - xverb-id: XUndoToLabel, fresh_document

  # do any other handling
  # Inkscape have a lot of useful "verbs"
  - verb-id: FileQuit

List of verbs

"verbs" is developed for Inkscape menu system, so "verbs" does not have any arguments. List of Inkscape "verbs" can be found at source code:
http://bazaar.launchpad.net/~inkscape.dev/inkscape/trunk/view/head:/src/verbs.cpp#L2543

List of xverbs

XFileSaveAs - save current document to specified filename
XFileOpen - open specified .svg filename instead of current document
XFileExportPNG - export to specified .png filename
XSelectElement - select svg element by name
XUndoLabel - set undo label
UndoToLabel - undo to specified label

Additional info

Some additional info can be found at maillist thread:
https://sourceforge.net/p/inkscape/mailman/inkscape-devel/thread/33487d06-e3c1-a4e5-1496-7b370d672d2f%40gmail.com/#msg35392523