VariableNames
In rules(md).ini
This section comprises a list of all Global Variables available in the game. Global Variables are boolean variables, their state is preserved between missions, but not saved in savegames.
In Maps
This section comprises a list of all Local Variables available in this map. Local Variables are boolean variables, their state is saved in savegames, but not carried over between missions.
Best of Both Worlds (Blade's post)
It is (theoretically) possible to carry an event (say capture a battle lab) through to having an effect on some later level (say allowing you to build a certain unit you normally cannot), but it is frustrated by the auto save feature that saves at the start of a level.
During a level, have some event you want to carry forward set a 'Local'. These are known to be carried by saves games as a nessesity. When the win condition is met, actually have two win triggers that have the 'Local' set or clear as one of the conditions. The clear one just triggers the win, while the set one sets a 'global' as well triggering the win. This will carry over to the next level and the player cannot save in the mean time to wipe it out (only the auto save can...maybe). In the next level, have a trigger that sets a new 'Local' to carry the 'global' during the level if the 'global' is set at the start of the mission. Just repeat this over as many levels as needed in order to carry the value to the level where it will have its effect. I've never really tested this and it remains just a theory of mine and I don't really know if autosave would save before or after the 'global variable' has had chance to convert to a 'local variable' so it remains a potential spanner in the works.