code: public double getDouble(String name, String namespace, double defaultValue) {
          String v = get(name, namespace);
          return v != null ? Double.parseDouble(v) : defaultValue;
      }
docs: Returns the attribute as a double value or the default.
  @param name the attribute name
  @param namespace the attribute namespace
  @param defaultValue the default if the attribute is missing
  @return the value