All
Checks to see if a field contains a value, or if all the fields in a list of fields contain values. If any of the fields is Null, then All returns False.
None
Checks that a field or list of fields have no value. None is the opposite of All.
AllOrNone
Checks if either all the field parameters have values, or none of them have values. Use this in cases where if an end user fills in one field, she must fill in all the other related values.
OnlyOne
Checks if exactly one field in the set has a value. Use this when the end user must fill in only one of a set of mutually exclusive fields.
OnlyOneOrNone
Checks if no more than one field in the set has a value. Use this in cases when a set of fields is both optional and mutually exclusive; that is, if the end user puts can put a value into one field in a set of fields, or leave them all empty.
