The recommended handler's 31990 coordinate 31990:pubkey:d.
Handler author pubkey extracted from the coordinate, if well-formed.
Handler d-tag identifier extracted from the coordinate, if present.
Optional platform marker the handler is recommended for (a-tag 4th element).
Optional relay-hint where the 31990 event can be found (a-tag 3rd element).
One handler endorsement parsed from a 31989
atag.