+* A suffix '@' followed by a date specification enclosed in a brace
+ pair (e.g. '\{yesterday\}', '\{1 month 2 weeks 3 days 1 hour 1
+ second ago\}' or '\{1979-02-26 18:30:00\}') to specify the value
+ of the ref at a prior point in time. This suffix may only be
+ used immediately following a ref name and the ref must have an
+ existing log ($GIT_DIR/logs/<ref>).
+