code: function parseProperty (value, propDefinition) {
    // Use default value if value is falsy.
    if (value === undefined || value === null || value === '') {
      value = propDefinition.default;
      if (Array.isArray(value)) { value = value.slice(); }
    }
    // Invoke property type parser.
    return propDefinition.parse(value, propDefinition.default);
  }
docs: Deserialize a single property.