How to add enum filter with All element

Sometimes customers request a specific filter in a form. The filter is based on an enum and must have All element to display all records regardless of field value. For example, a filter has 3 elements: All, Quotation, Order; although enum has only 2 elements: Quotation, Order.

Problem description
Analyse how All element is added to an enum filter in standard AX.

Hints
To answer the question let's search for enums with All element and Filter suffix in standard AX.

How to make enum a mandatory field on a table

It seems obvious, just set Mandatory property on a field to Yes. Is it enough? No.

Problem description
Null value concept is important for a mandatory field, but null values are not supported in Dynamics AX. Instead there are default values for each data type and they are considered null.
For enum it is an element with value set to 0. An assumption can be made that it shouldn't be possible to select and save enum element with value 0 on mandatory field. MSDN post proves the assumption:
"when the validateField method checks whether a user has entered a value in a mandatory field ...
the first entry is not accepted in an enum type field".
In another MSDN post there is an alternative requirement:
"If you want to make an enum a mandatory field on a table, make the first outcome with the value zero, as none, with the label Not selected"
What is correct? Let's analyse. You can also jump to the conclusion section.