The Plot>Set Legend... command brings up a dialog into which you can type a
legend (the large text displayed at the top of the picture).  
Certain character sequences in this
string will be automatically replaced by other information when the legend is
displayed:

%T    Time, e.g. "250.25 hours"

%q    Name of the quantity currently being plotted.

%m    A list of all factors currently at mutant levels, or "WILDTYPE" if
the wild type is being run.  If no factors have mutant levels defined,
this is replaced by the empty string.

%c for any other character c: the character c is inserted.

\n    A newline character.

\c for any other character c: the character c is inserted.

The default string can be restored with the "Get default" button in the dialog.

The command-line equivalent is

    m = leaf_setproperty( m, 'legendTemplate', ... );

