If this is prior to min_date, sets this equal to
min_date.
If this falls after max_date, sets this equal to
max_date. Otherwise, this is unchanged. Either of min_date and max_date
may be null. All non-null dates must be
valid.
| this |
a Date to clamp |
| min_date |
minimum accepted value for this |
| max_date |
maximum accepted value for this |