sS unicode_mathBoldScript(S s) {
  new StringBuilder buf;
  for (char c : characters(s)) {
    if (c >= 'a' && c <= 'z')
      buf.append(unicode_mathBoldScript_aToZ_lower(c));
    else if (c >= 'A' && c <= 'Z')
      buf.append(unicode_mathBoldScript_aToZ_upper(c));
    else
      buf.append(c);
  }
  ret str(buf);
}

Began life as a copy of #1024069