Our dev group have found benefits in using the `postMessage` event as a
great way to do pub/sub type communication. We'd love to use it in
Launch, but don't see a way to make it work outside of Custom Code. Is
Custom Code the only way to do it? It would be great to have an Event
Type where we could select `postMessage` and then be asked for a string
for it to look for inside of a data, so `siteEventName` in the example
below. The data name would need to be standardized on, or also make that
some...
