better documentation for -P

man/man8/zfs.8

@@ -2600,7 +2600,31 @@ options and those implied by other options.
 The actual dataset creation can still fail due to insufficient privileges or
 available capacity.
 .It Fl P
-Print machine-parseable verbose information about the created dataset.
+Print machine-parsable verbose information about the created dataset.
+Each line of output contains a key and one or two values, all separated by tabs.
+The
+.Sy create_ancestors
+and 
+.Sy create
+keys have
+.Em filesystem
+as their only value.
+The
+.Sy create_ancestors
+key only appears if the
+.Fl p
+option is used.
+The
+.Sy property
+key has two values, a property name that property's value.
+The
+.Sy property
+key may appear zero or more times, once for each property that will be set local
+to
+.Em filesystem
+due to the use of the
+.Fl o
+option.
 .It Fl v
 Print verbose information about the created dataset.
 .El
@@ -2674,7 +2698,35 @@ options and those implied by other options.
 The actual dataset creation can still fail due to insufficient privileges or
 available capacity.
 .It Fl P
-Print machine-parseable verbose information about the created dataset.
+Print machine-parsable verbose information about the created dataset.
+Each line of output contains a key and one or two values, all separated by tabs.
+The
+.Sy create_ancestors
+and 
+.Sy create
+keys have
+.Em volume
+as their only value.
+The
+.Sy create_ancestors
+key only appears if the
+.Fl p
+option is used.
+The
+.Sy property
+key has two values, a property name that property's value.
+The
+.Sy property
+key may appear zero or more times, once for each property that will be set local
+to
+.Em volume
+due to the use of the
+.Fl b
+or
+.Fl o
+options, as well as
+.Sy refreservation
+if the volume is not sparse.
 .It Fl v
 Print verbose information about the created dataset.
 .El