Perhaps some visual illustrations will cement these concepts. Here is the Type hierarchy browser from Base enum TableGroupAll, showing not just how ItemCode extends TableGroupAll, and how PriceDiscitemCode extends ItemCode, but just how many other EDT's are extended from each other in this tree. When I say that TableGroupAll is a common Base enum in AX, I'm not kidding! In the right pane each of the properties is listed in rows, showing how each EDT inherits from the one it extends, as shown from right to left. Note that TableGroupAll has a Label of @SYS17743, but ItemCode overrides that Label with @SYS58740, and further how TableGroupAll does not have a HelpText at all, but PriceDiscItemCode has a HelpText of @SYS20804. Here is the PriceDiscAdmTrans form, more commonly know as the Price/discount journal lines. Here we can see the ItemCode field, which has a type of PriceDiscItemCode. The values of Table, Group, and All, inherit from the Base enum TableGroupAll, while the Label of "Item code" inherits from the EDT of ItemCode, and the HelpText at the bottom from EDT PriceDiscItemCode. That is the essence of inheritance.
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