See these pages for some embedded notes on learning the interface and some of its variations. I'm starting on Google Chrome / Windows 10 and that typically means "Ctrl" is the modifier key, not "Cmd" or "Alt".
Names of Things and Interface Names and Plugin Names and About Assets Plugin.
Item adds some notes to my local copy about inspecting items in a page. **Notably Ctrl-I/Cmd-I in an item editor gives you "About".**
Single Page Wumpus uses the Assets Plugin and the Frame Plugin - About Frame Plugin for an SVG.
The page Jeff Miller uses the Assets and HTML plugins for icons and links to profile pages on C2 Wiki, GitHub, Twitter.
Jeff Learns To Make Plugins will collect some notes about making plugins. Ward gave me some starting places and Eric provided examples from his site. Please reconstruct under the title Jeff Learns To Make Plugins
Learning Phototelling talks about working with the script-driven pages linked from and embedded in Phototelling Quickstart.