When a macro is fetched from a library, for instance the macro "View/t" which is very often used, its structure is duplicated in memory in the user's window and thus takes quite a lot of space. It is not necessary to save this structure in the user's disk file as it can always be found in the library. This is exactly what is done : MUSTIG does not save macro definitions in a file when they come from the library (except when the option Edit / Options / Save all graph has been chosen. The Save all mode is attractive if you work with a customized version of a library and you want to exchange files with other users).

The notion of sub-program in a disk file is rather delicate : if the user modifies the content of the macro extracted from the library, or if he makes an image of a box within the macro, the part belonging to the user will be saved.