In this tutorial, a list will be referenced. You can get the list here, or from inside the plugin jar.

At the top of the list, there is the following:

hilly:
    nopopulate:
        type: flag
        description: Setting this flag will disable populators

Walking through each line, this shows that the hilly generator can use the nopopulate flag in its options, which will disable populators. There are four types used in BananaGen: flag, string, integer, and double.

• flags have no value and are either set or not set. For example, a generator could be defined as hilly,nopopulate to use the hilly generator but disable populators.

• strings have a text value, like SAND.

• integers and doubles are numbers, whole or with a decimal point, respectively. Sometimes there are minimum and maximum values.

    waterlevel:
        type: integer
        description: Up to this height, valleys made by the base chunk generator will be filled with liquid (water normally, lava for nether)
        default: 64
        min: 0
        max: 127
  

Walking through this example, we see that the waterlevel integer will change the height of water the generator makes. It starts (default) at 64, but you can put it anywhere from (min) 0 to (max) 127.

Here are a few visual examples:

Both images are generated using the hilly generator with the same seed (1795116593915449260 for anyone who's interested). The top image was made using hilly, and the bottom image was made using hilly,nether. This shows how a simple change can drastically alter how a world looks without changing the basic shape of the terrain.