As binary formats go, UTF-8 is extremely tame. Some of the complexities that binary formats love to throw at you:

* Things may be non-byte-aligned bitstreams.

* Arrays of structures that go "read until id is 5, but if id is 5, nothing else of the structure is emitted."

* Fields that may be optional if some parent of the current record has some weird value.

* Files may be composed of records at arbitrary, random offsets that essentially require seeking to make any sense of it.

* The metadata of your structure may depend on some early parameter (for example, is this field big-endian or little-endian?)

and so on.

File formats like ELF (supporting ELF32, ELF64, and both little-endian and big-endian, all in a single format definition) or Java class files (long and double entries in the constant pool take up two slots, not one) are a better guideline for how powerful the format is in handling weirder idiosyncracies.