docs(config): derived variables in the EDIT screen #21

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allan merged 23 commits from docs/derived-variables into main 2026-10-21 22:26:31 +00:00
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@@ -78,6 +78,8 @@ Derived columns themselves are an EDIT screen feature: the VIEW screen and the d
A configuration error - a bad name, an invalid type or length, a name collision, or a reference to a derived variable that is not defined earlier - stops the EDIT screen with a message naming the variable. A syntax error or an unknown column in the expression itself is caught when the view is compiled, and stops the screen with a message naming the table.
Most of these rules are also applied when a row is submitted for approval, through a post edit hook on `MPE_DERIVED`. A bad name, type, length, format or expression - or a duplicate name, or a reference to a variable that is not defined earlier - is rejected at submit time, while the error can still be corrected, rather than breaking the EDIT screen afterwards. The collision between `VAR_NM` and a physical column of the target table is only checked at read time, as the hook does not have the target library assigned.
!!! warning "Derived values can expose hidden data"
An expression can reference a column that is hidden from the user by [Column Level Security](/column-level-security/), and the derived column will show the result. Configure derived variables with the same care as any other data exposure.