What are plotly.express, plotly.io, and plotly.go and when do we use them?

What are plotly.express, plotly.io, and plotly.go and when do we use them? I keep running into them in the Plotly documentation, but I can't really figure out what the differences are. My guess is that plotly.express is the most general-use part of the plotly API and plotly.go is used more commonly when you want to publish a graph as HTML or in some other format, but I suspect that this crude impression is incorrect. Any thoughts, comments, or general advice is appreciated. Thanks.