code: private Schema readInnerSchema(JsonReader reader, String key, Set<String> knownRecords) throws IOException {
      if (!key.equals(reader.nextName())) {
        throw new IOException("Property \"" + key + "\" missing.");
      }
      return read(reader, knownRecords);
    }
docs: Constructs a {@link Schema} from the "key":"schema" pair.
  
  @param reader The {@link JsonReader} for streaming json input tokens.
  @param key The json property name that need to match.
  @param knownRecords Set of record name already encountered during the reading.
  @return A {@link Schema} object representing the schema of the json input.
  @throws java.io.IOException When fails to construct a valid schema from the input.