A folder is a convenience primitive that allows you to
group sets of primitives together. For instance, if you had an ecological
predator prey model, you could group all the predator primitives together in a
folder and do the same for the prey primitives. This helps to keep complex
models organized. Folders group primitives together in the library browser and
by default they also do so in the model diagram. However, the latter grouping
can easily be disabled.
Additionally, you can disable or enable entire folders (or individual primitives) by selecting the checkbox next to the folder in the primitive browser on the left of the main screen. Disabled primitives will not be included in the simulation when the model is run. This allows you to test specific portions of your model in isolation. Just make sure you do not disable a section of the model that is required by a part that is still enabled!
Example of Enabled and disabled Primitives
In the example model illustrated above, only the stock A will be enabled when the model is run. Although stock C is set to be enabled, it is in a disabled folder so it also becomes disabled. The model diagram accurately shows which parts of the model are enabled and disabled.