code: public void put(final Properties properties) {
      for (final String propName : properties.stringPropertyNames()) {
        this._current.put(propName, properties.getProperty(propName));
      }
    }
docs: Put the given Properties into the Props. This method performs any variable substitution in the
  value replacing any occurrence of ${name} with the value of get("name"). get() is called first
  on the Props and next on the Properties object.
  
  @param properties The properties to put
  @throws IllegalArgumentException If the variable given for substitution is not a valid key in
  this Props.