Mail · Reading: a message reader, a conversation, and quoted text

MailReader opens a message under its subject: the sender's picture,
name and address, who it went to, when it came, and Reply, Reply all
when it went to more than one, and Forward, each only with a handler;
then its words and its files, each downloadable. MailThreadView lays a
conversation oldest first: the newest stands open, the others fold to
a line of the sender, their first words and when, which a press, Enter
or Space opens. QuotedText folds words quoted from before behind a
small mark; open, they sit behind a rule. Long names give way at the
label width.

tasks/ch21-30.md

@@ -369,9 +369,9 @@
 
 ## T29b Mail · Reading
 
-- [ ] MailReader
-- [ ] MailThreadView
-- [ ] QuotedText
+- [x] MailReader
+- [x] MailThreadView
+- [x] QuotedText
 
 ## T29c Mail · Writing