# properties.email.description
The account email. A verification link is sent to it — the account cannot send email until the address is verified, which is what makes registering safe without a password.

# properties.channel.description
Distribution-channel slug this registration came through (e.g. wordpress-plugin). Invalid values are dropped, never an error.

# properties.ref.description
Referral code of the account that referred this signup, when any.

# properties.referrer.description
First-touch landing referrer URL, when known. Invalid values are dropped, never an error.