Important: ====> context variables are described here.
A formula must return a value which is appropriate for its column. For instance, a formula for a string column must return a string. Numeric types are automatically converted as needed.
If a formula returns nothing, then the value of the column is unchanged:
Formulas can access the values of the current row, and the old row, as well as the current values of parent rows. They must not access the values of grandparent rows.
Validation rules must evaluate to a boolean value. If a validation rule does not return a boolean value, an error will result.
Like formulas, validations can access the values of the current row, the old row, and any parent rows.
Events do not have to return any value -- if they do, that value will be ignored.
Like formulas and validations, events can access the values of the current row, the old row, and any parent rows.