Using IntelliSense
One of the challenges of using any code base is discovering what's available. Happily, IntelliSense is supported for JavaScript programming, which provides you with an opportunity to discover the vast library of features available for script programming. You can use IntelliSense while writing code and debugging.
To ensure that you see all available features, in Visual Studio choose Tools > Options > Text Editor and uncheck the option "Hide Advanced members" to reveal some hidden advanced features of the .NET Framework.
Visual Studio dynamically discovers all the properties of the voice object, which is an instance of the SAPI.SpVoice ActiveX object. Using IntelliSense, you can find out the names of members. Even if you have no previous experience with a member, you can Google the member names; you'll usually find a blog, article, or book reference that will provide a code example.