used immediately following a ref name and the ref must have an
existing log ($GIT_DIR/logs/<ref>).
+* A ref followed by the suffix '@' with an ordinal specification
+ enclosed in a brace pair (e.g. '\{1\}', '\{15\}') to specify
+ the n-th prior value of that ref. For example 'master@\{1\}'
+ is the immediate prior value of 'master' while 'master@\{5\}'
+ is the 5th prior value of 'master'. This suffix may only be used
+ immediately following a ref name and the ref must have an existing
+ log ($GIT_DIR/logs/<ref>).
+
* A suffix '{caret}' to a revision parameter means the first parent of
that commit object. '{caret}<n>' means the <n>th parent (i.e.
'rev{caret}'