Create a catalogue of includable elements

[mgrabovsky]

t would be nice to have a catalogue of the various gadgets that we use in our texts (e.g. “figure”, “expander”, “preview block”, etc.) so that we can see them all in one place. This could

• make it easier to find the right one for a specific need, but also
• allow for a unification/standardisation in design and usage at some point.