{{ 'hello' | upcase }} uses the upcase filter, when inserted into an options block it will render HELLO. You can string multiple Liquid filters together, with the expression processed left-to-right.
You can find our variables on the following pages:
Examples
Get the Current Date and Time in yyyymmdd Format
Expression:{{ "now" | date: "%Y-%m-%d" }}
Sample result: “2018-04-24”
Reference
Get the Size of an Array and Multiply by 10
Expression:{{ .my_array | size | times: 10 }}
Sample result: 50
Reference