Dates in DBgrids - AArg !

I have for some time now been developing a program for one of our
departments which has to be completely bomb-proof in its data
validation....

The problem is, I can't tell how the onvalidate event works, having
read the help which is as usual somewhat opaque.

Does anyone have an example of the onvalidate event, particularly used
for date fields, even more particularly a dbgrid date field.

TIA.