docs: private static Headers combine(Headers cachedHeaders, Headers networkHeaders) {
      Headers.Builder result = new Headers.Builder();
  
      for (int i = 0, size = cachedHeaders.size(); i < size; i++) {
        String fieldName = cachedHeaders.name(i);
        String value = cachedHeaders.value(i);
        if ("Warning".equalsIgnoreCase(fieldName) && value.startsWith("1")) {
          continue; // Drop 100-level freshness warnings.
        }
        if (isContentSpecificHeader(fieldName)
            || !isEndToEnd(fieldName)
            || networkHeaders.get(fieldName) == null) {
          addHeaderLenient(result, fieldName, value);
        }
      }
  
      for (int i = 0, size = networkHeaders.size(); i < size; i++) {
        String fieldName = networkHeaders.name(i);
        if (!isContentSpecificHeader(fieldName) && isEndToEnd(fieldName)) {
          addHeaderLenient(result, fieldName, networkHeaders.value(i));
        }
      }
  
      return result.build();
    }