Att Dirties

Analytica sets this flag on system variables to mark whether a change to the system variable should dirty the model, which would cause the Save option to become enabled on the File menu. It is read-only on these.

Starting with Analytica 6.6, you can set this attribute on user variables (but only user variables). When it is set it tells Analytica that a change to the Definition should not "dirty" the containing module or library. This allows you to have a user input variable, on a variable that holds internal state, in a filed library where you don't want models using the library to change the library file itself (but you might want the user to change the user input or internal state).