sclass NLStringMatcher_dollarVars_underscores_dollarDollar extends StringMatcher {
  // change matches only if returning true
  bool match(S pat, S input, SS matches) {
    pat = trim(pat);
    // full-string match with $$x
    if (startsWith(pat, "$$") && isDollarVar(pat))
      ret strictPutIC(matches, pat, input);
      
    SS newMatches = matchDollarVarsIC_underscores(pat, input);
    ret newMatches != null && addMapToMapWithoutOverwritingIC(matches, newMatches);
  }
  
  S apply(S input, SS matches) {
    ret replaceVars(input, matches);
  }
}

Began life as a copy of #1017696