Good news! The "Input Text" box is editable. You can click any of the pre-made generators and edit them, or write your own.
Your changes are never saved. Whether you write your own script, or edit one of the pre-made ones, if you close the browser, leave this page, or click on one of the pre-made generators, your work will be lost.
I strongly recommend writing your script in a text file or word processing document that's saved at your end, whose contents you can copy and paste into the Input Text box whenever you want to use it.
Here's a very basic input script:
We have two lists here - #MAIN and #DOG.
The randomizer will always look for a list called #MAIN. It will pick a random entry from under that #MAIN heading - i.e. cat, goldfish, <DOG>, or hyena. For most of those entries, it'll simply return the result.
If it lands on <DOG>, instead of just returning "<DOG>", it'll look for a #DOG list, and return a random entry from that.
A few characters have special effects. If a line begins with one of them, you'll get special behaviours out of the generator:
If you see a line beginning with ! or %!, that's just me signalling something to myself. Don't worry about it.
Also: The list titles don't have to be in all-caps. However, they are case-sensitive.
Also also: You can resize the text area by clicking and dragging the lower-right corner.