endorse-label is a separate program that
handles requests for deferral of trust. It takes a rater and a
label bureau as arguments and contacts the label bureau to request
labels from the specified rater that vouch for the author of each
of the statements on STATEMENT-LIST. When GoodMouseClicking is
found to vouch for a statement's author, GoodMouseClicking's identifier
is added to the beginning of that statement, and the new statement
is returned, to be added to the caller's STATEMENT-LIST. As in the previous
examples, the match expression then searches the statement
list, in this case for a statement added by the endorse-label
program that begins with "mailto:GoodMouseClicking@w3.org."
The same principle can be used to insist on signed labels, in
case we are worried about forgeries. Instead of invoking
endorse-labels,
we could invoke a module that checks a digital signature or performs
other types of cryptographic checks.