class_docstr: Mixin class for Cartesian 1D Chart elements to add basic support for
  SelectionExpr streams.
class_docstr_tok: ["Mixin","class","for","Cartesian","1D","Chart","elements","to","add","basic","support","for","SelectionExpr","streams","."]
code: def _empty_region(self):
      invert_axes = self.opts.get("plot").kwargs.get(
          "invert_axes", False
      )
      if (invert_axes and not self._inverted_expr) or (
          not invert_axes and self._inverted_expr
      ):
          region_el = HSpan
      else:
          region_el = VSpan
      return NdOverlay({0: region_el()})
  
imports: import sys
  import numpy
  import pandas
  from ..core import Dataset, NdOverlay, util
  from ..streams import Lasso, Selection1D, SelectionXY
  from ..util.transform import dim
  from .annotation import HSpan, VSpan
label_desc: Use image node_id 1 for calling the Selection1DExpr obj's underlying member method code with example usage: obj._empty_region() and returns: NdOverlay