Tested in Automatic1111 (and most in ComfyUI). Reference: https://www.youtube.com/watch?v=MgLpmksylOc&t=482s

Syntax	Example	Behaviour
[a|b]	[cat|dog]	Alternatively will use cat and dog for every step
[a|a|a|b]	[cat|cat|cat|dog]	Will use cat for every step, except each fourth step, which will be dog
[from:to:when]	[cat:dog:10] [cat:dog:.6]	Will use cat for the first 10 steps and then switch to dog Will use cat for the first 60% of the steps and then switch to dog
[from::when]	[cat::10]	Wil use cat for the first 10 steps and nothing after that – of course only useful when there still is another piece of prompting
[to:when]	[cat:20]	Starts using cat only after 20 steps