code: def _anchor(self, adjustment):
      (
          adv,
          dx,
          dy,
          adv_adjust_by,
          dx_adjust_by,
          dy_adjust_by,
      ) = adjustment
  
      assert not adv_adjust_by
      dx_device = dx_adjust_by and dx_adjust_by.items() or None
      dy_device = dy_adjust_by and dy_adjust_by.items() or None
  
      return ast.Anchor(
          dx or 0,
          dy or 0,
          xDeviceTable=dx_device or None,
          yDeviceTable=dy_device or None,
      )
  
imports: import logging
  import re
  from io import StringIO
  from fontTools.feaLib import ast
  from fontTools.ttLib import TTFont, TTLibError
  from fontTools.voltLib import ast
  from fontTools.voltLib.parser import Parser
label_desc: Use image node_id 17 for calling the VoltToFea obj's underlying member method code with example usage: obj._anchor(adjustment) and returns: ast