How to use [slot.description]

The reference page of slot.description has its arguments, constraints and declaration.

Returns the description of a single compiled slot, given its name as the value of the slot, or an expression leading to its name.

slot.description:while

The above returns the value “Repeats execution while a condition is true”. The slot throws an exception if no slot name is supplied, or if the slot does not exist. Inside a [whitelist] invocation, it will also throw for slots the whitelist does not allow.