Excel has a feature called Validation [found under (D)ata
(V)alidation.

When used, it prevents a user from entering data that doesn't meet a
set of user-defined conditions (i.e. number is <> x, a list of
acceptable input, etc.).

I am trying to figure out a way to invoke this feature if a certain
condition applies.

For example:  Cell A2 contains the value "1".  I want a conditional
validation on cell A1; so that if cell A2 is greater than 0, then
invoke the validation feature, else, ignore the validation feature and
allow an entry.

Cell A1 needs to validate (allow) a number between 1 and 100, ELSE,
disallow the entry.

Any help would be appreciated.  Thank you.