hscale=auto;

a->b: Not numbered;
a->b: Numbered [number=yes];
a->b: Numbered [number=10];
a->b: Not numbered;
numbering=yes;
a->b: \bNumber is bold;
a->b: \|\bNumber is not bold;
a->b: Our number is: \N;
a->b: (\N) This may be optional;
numbering.pre="Step #";
numbering.post=" is: ";
a->b: Some action;
a->b: Some action;
numbering.pre="\c(red)\b";
numbering.post=": \s()";
a->b: Some action;
a->b: \c(blue)\uSome action;
a->b: \|\c(blue)\uSome action;