Ability to prevent user from choosing a date later than today's date in a custom date field

[#1]

Whether in custom fields or system fields, would love to have the capacity to enable whether user can choose a date later than today's date. Entered on behalf of Lindsay Wescott.

[#2]

This would be huge for us in our org. We have integrations that rely on campaign reporting start and end dates. sloppy end users put in end dates before the start dates... validation would be very helpful!