Comments are posted through the email interface, just by sending the message to special address. For example:
$ mutt "mailto:comment@blog.example.com?subject=BlaBlaBla%20(576540a5b98517b46d0efc791bb90b9121bf147e)" <<EOF This is the comments contents. Could be multilined of course. EOF
Comments are stored in Git as a note. Those objects could be updated without touching the base commit itself.
Each comment is just a plaintext with From and Date
headers. From is a name of email sender (with email address
stripped off).
Only text/plain or multipart/signed+text/plain email
messages are accepted and only with UTF-8, US-ASCII, ISO-8859-1
character sets. Sane people won’t send HTML email anyway, but this is
just a precaution.
Comments are stored in recfiles – GNU recutils human-editable plaintext database format. But they do not contain records description:
%rec: Comment %doc: SGBlog's comment %mandatory: From Date Body %type: Date date