Variable: icalendar-uid-format

icalendar-uid-format is a customizable variable defined in icalendar.el.gz.

Value

"emacs%t%c"

Documentation

Format of unique ID code (UID) for each iCalendar object.

The following specifiers are available:
%c COUNTER, an integer value that is increased each time a uid is
   generated. This may be necessary for systems which do not
   provide time-resolution finer than a second.
%h HASH, a hash value of the diary entry,
%s DTSTART, the start date (excluding time) of the diary entry,
%t TIMESTAMP, a unique creation timestamp,
%u USERNAME, the variable user-login-name(var)/user-login-name(fun).

For example, a value of "%s_%h@mydomain.com" will generate a UID code for each entry composed of the time of the event, a hash code for the event, and your personal domain name.

Source Code

;; Defined in /usr/src/emacs/lisp/calendar/icalendar.el.gz
(defcustom icalendar-uid-format
  "emacs%t%c"
  "Format of unique ID code (UID) for each iCalendar object.
The following specifiers are available:
%c COUNTER, an integer value that is increased each time a uid is
   generated.  This may be necessary for systems which do not
   provide time-resolution finer than a second.
%h HASH, a hash value of the diary entry,
%s DTSTART, the start date (excluding time) of the diary entry,
%t TIMESTAMP, a unique creation timestamp,
%u USERNAME, the variable `user-login-name'.

For example, a value of \"%s_%h@mydomain.com\" will generate a
UID code for each entry composed of the time of the event, a hash
code for the event, and your personal domain name."
  :type 'string
  :group 'icalendar)