Nearly everything inherits from a basic struct that is 8 bytes per atom: { length of self + children, quasi-human readable 4 char code describing contents }

Practically speaking, in C/C++, you can stride by length and switch() on the ftype, using it to cast the read-in data to whatever class/struct you desire.

All of this while being so brutally dumb that you can rewrite it over and over again in about 10 lines of code in most languages.