* captured.
*
* The reference is stored as a #GstCaps in @reference. Examples of valid
- * references would be `timestamp/x-drivername-stream` for timestamps that are locally
- * generated by some driver named `drivername` when generating the stream,
- * e.g. based on a frame counter, or `timestamp/x-ntp, host=pool.ntp.org,
- * port=123` for timestamps based on a specific NTP server.
+ * references would be
+ *
+ * * `timestamp/x-drivername-stream`: for timestamps that are locally
+ * generated by some driver named `drivername` when generating the stream,
+ * e.g. based on a frame counter
+ * * `timestamp/x-ntp, host=pool.ntp.org, port=123`: for timestamps based on a
+ * specific NTP server. Note that the host/port parameters might not always
+ * be given.
+ * * `timestamp/x-ptp, version=IEEE1588-2008, domain=1`: for timestamps based
+ * on a given PTP clock.
+ * * `timestamp/x-unix`: for timestamps based on the UNIX epoch according to
+ * the local clock.
*
* Since: 1.14
*/