Warn user about custom handler's tags potentially conflicting with default handlers #53
Description
As a new user of transit, it wasn't obvious to me that default handler's tags share the same namespace as my custom tags.
It makes sense now, but hindsight is 20/20...
Ideally for me, a warning should be issued when trying to add a handler on a tag that already denotes another type, but the current "late binding" api doesn't seem amenable to this.
Instead, I would suggest adding a warning in the documentation of write-handler reminding the user to check for conflicts with previously declared tags (default or otherwise). Ideally pointing to the spec page on github where said default tags are easily visible.
Happy to contribute this if there's consensus!