In "The Swift Programming Language (Swift 5.6 beta)" by Apple, in the Language Reference/Statements section, there is a formal definition of a guard statement

guard <condition> else {
  <statements>
}

where, I quote “...The value of any condition in a guard statement must be of type Bool or a type bridged to Bool. The condition can also be an optional binding declaration, as discussed in Optional Binding...”

What does it mean for a type to be bridged to Bool (or to whatever other type T assuming bridging to T is possible)? Is this something specific to Bool, like an implicit cast? Is it a built-in or can one generally bridge to any T by following a formal procedure.

I've searched far and wide but have not been able to find a formal-ish description of bridging in the same publication or elsewhere (if one exists please point it out to me).