`switch_case`

Toggles the case of all selected letters.

--- Examples ---

┌───────────────────────┐     ┌───────────────────────┐
│ [t]his is a sentence. │ --> │ [T]his is a sentence. │
└───────────────────────┘     └───────────────────────┘

┌───────────────────────┐     ┌───────────────────────┐
│ (tHIS] is a sentence. │ --> │ (This] is a sentence. │
└───────────────────────┘     └───────────────────────┘