code: def addLookupReferences(
      feature, lookups, script=None, languages=None, exclude_dflt=False
  ):
      
      assert lookups
      if not script:
          for lookup in lookups:
              feature.statements.append(ast.LookupReferenceStatement(lookup))
          return
  
      feature.statements.append(ast.ScriptStatement(script))
      if exclude_dflt:
          for language in languages or ("dflt",):
              feature.statements.append(
                  ast.LanguageStatement(language, include_default=False)
              )
              for lookup in lookups:
                  feature.statements.append(ast.LookupReferenceStatement(lookup))
      else:
          feature.statements.append(
              ast.LanguageStatement("dflt", include_default=True)
          )
          for lookup in lookups:
              feature.statements.append(ast.LookupReferenceStatement(lookup))
          for language in languages or ():
              if language == "dflt":
                  continue
              feature.statements.append(
                  ast.LanguageStatement(language, include_default=True)
              )
docs: Add references to named lookups to the feature's statements.
      If `script` (str) and `languages` (sequence of str) are provided,
      only register the lookup for the given script and languages,
      optionally with `exclude_dflt` directive.
      Otherwise add a global reference which will be registered for all
      the scripts and languages in the feature file's `languagesystems`
      statements.