+ begin
+ Parse_Expression
+ (In_Tree => In_Tree,
+ Expression => Field_Id,
+ Flags => Flags,
+ Current_Project => Current_Project,
+ Current_Package => Current_Package,
+ Optional_Index => False);
+
+ if Expression_Kind_Of (Field_Id, In_Tree) = List then
+ Error_Msg
+ (Flags, "expression must be a single string", Loc);
+ else
+ Set_External_Default_Of
+ (External_Value, In_Tree, To => Field_Id);
+ end if;
+ end;