docs: public String replaceSymbols(String str) {
          Matcher m = SYMBOL_DEF.matcher(str);
          if (m.find()) {
              String symbol = m.group(1);
              String expansion = get(symbol);
              if (expansion != null) {
                  return str.replace(m.group(0), expansion);
              }
          }
  
          return str;
      }