Comment by tom_

With the disclaimer that I let my language lawyer qualification lapse a while ago, it's broadly to do with the character types being the only approved way to examine the bytes of an object. An object of a type can be accessed only as if it were an object of that type or some compatible type, but: it can also be accessed as a sequence of characters. (You'd do this if implementing memcpy, memset or memcmp, for example.)

6.2.6.1 - only character types can be used to inspect the sequence of bytes making up an objuect, and (interestingly) only an array of unsigned char is suitable for memcpy'ing an object into for inspection. It's possible for sequences of bytes to exist that don't represent a valid value of the original object; it's undefined behaviour to read those sequences of bytes other than via a character type (i.e., I think, via a pointer to something compatible with the object's actual type - there being no other valid ways to even attempt to read it)

6.3.2.3 - when casting a pointer to an object type to a pointer to a character type, the new character pointer points to the bytes of the object. If converting between object types, on the other hand, the original pointer will (with care) round trip, and that seems to be all you can do, and actual access is not permitted

6.5.1 - as well as all the expected ways of accessing an object, objects can be accessed via a character pointer