class_docstr: Base class for options settings used to specified collections of
  keyword options.
class_docstr_tok: ["Base","class","for","options","settings","used","to","specified","collections","of","keyword","options","."]
docstr: Allows subclasses to check options are valid.
docstr_tok: ["Allows","subclasses","to","check","options","are","valid","."]
code: def _validate(cls, options, items, warnfn):
      "Allows subclasses to check options are valid."
      raise NotImplementedError(
          "KeywordSettings is an abstract base class."
      )
  
imports: from collections import defaultdict
  from ..core import Store
label_desc: Use image node_id 3 for calling the KeywordSettings obj's underlying member method code with example usage: obj._validate(cls, options, items, warnfn) without return types