src/third_party/web_platform_tests/resources/webidl2/test/syntax/idl/operation-optional-arg.widl

// Extracted from http://dev.w3.org/2006/webapi/WebIDL/ on 2011-05-06
interface ColorCreator {
  object createColor(float v1, float v2, float v3, optional float alpha = 3.5);
};