# Constants
DateOnly represents the 'dateonly' format (YYYY-MM-DD) (`validate:"date=dateonly"`).
DateTime represents the 'datetime' format (YYYY-MM-DD HH:MM:SS) (`validate:"date=datetime"`).
DateValidatorTag is the tag identifier for date validation (`validate:"date={formats}"`).
RFC3339 represents the 'rfc3339' format (YYYY-MM-DDTHH:MM:SSZ, YYYY-MM-DDTHH:MM:SS±HH:MM) (`validate:"date=rfc3339"`).
TimeOnly represents the 'timeonly' format (HH:MM:SS) (`validate:"date=timeonly"`).
# Structs
DateValidator implements the CustomValidator interface for date validation.