Writer "Show variable" from Custom Properties?

users
#1

The current Writer Guide (WG60, I believe) says that one way to define variables (particularly, but not limited to, text values) for use in a document is in "Custom Properties"
  (File > Properties > Custom Properties).
Unfortunately, variables so defined do not show in the "Show variables" list
  (Insert > Field > More Fields > Variables > Show variable).
So how are those variables inserted as text fields in the document? AFAICS neither Writer Help nor WG60 covers this question.

Also not covered (AFAICS) is the use of DDE for text fields in the document. How is that done?

John

#2

The current Writer Guide (WG60, I believe) says that one way to define variables (particularly, but not limited to, text values) for use in a document is in "Custom Properties"
    (File > Properties > Custom Properties).
Unfortunately, variables so defined do not show in the "Show variables" list
    (Insert > Field > More Fields > Variables > Show variable).
So how are those variables inserted as text fields in the document?  AFAICS neither Writer Help nor WG60 covers this question.

Um, sorry for the list noise on this question. After a couple hours of not finding it in the referenced documentation (Help and WG60), I just found that variables defined in "Custom Properties" are treated differently from variables defined via Insert... .
  So, from Insert > Field > More Fields, the "Custom Properties" variables
    are inserted from the "DocInformation" tab > "Custom"
    rather than from the "Variables" tab > "Show variable".

But that raises new questions. For example: Isn't it a hazard to having two databases for the document's variables? For example, what happens if the same variable name is used in both places?

Also, I still have not found an answer to this:

Also not covered (AFAICS) is the use of DDE for text fields in the document. How is that done?

John