Custom inspectors

[mbostock]

Symbol.for("observablehq.display")? Ref. https://docs.deno.com/runtime/manual/tools/jupyter#rich-content-output, but in our case it should return an HTML element/node for insertion, rather than a string, since we’re running in the client and we don’t need serializable values.

[Fil]

related to #23 #1120

[mbostock]

For precedent there is also Symbol.for("nodejs.util.inspect.custom").

Another approach would be to register custom inspectors in the config.