Advanced Visio shapesheet training?

Do you know of educational resources for acquiring in-depth knowledge of Visio shapesheet functionality?

Visio has some very capable features through shapesheets, and the ability to customize is significant. I want to learn more about the inner workings and how to accomplish the scenarios I have planned out. However, I have not found any resources online that match my criteria. It’s all very basic touch-and-go kind of stuff.

Are you aware of any more solid educational resources? Please let me know!