Templates were a fixed subject and body, so anything that changed per
message -- who it is going to, today's date -- had to be typed over
afterwards.
Eight names are recognised: recipientName, recipientFirstName,
recipientEmail, myName, myEmail, subject, date and time. Dates and times
go through datetime.ts rather than toLocaleDateString, so a template
follows the date order and clock the app was already told to use.
Filling happens on insert rather than on send. What a placeholder came to
is then visible in the composer and can be edited, instead of the message
changing between writing it and sending it.
Two things are deliberately left alone. A placeholder that cannot be
answered yet -- a recipient's name on a draft nobody has addressed -- stays
in the body as written, because substituting an empty string produces
"Hi ,", which is wrong rather than visibly unfinished; leaving the name
says which word is still missing and can be typed over. And a name that is
not a placeholder is left as written too, since a body that quietly ate an
unrecognised token would be worse than one that shows it.
Values are escaped on the way into HTML: a display name comes from a
contact card or a typed address and is not trusted markup.
