byte order to write values with

what are we inside? (e.g. struct, variant, array)

position of array element type in type_str

whether to write values

position of length of the array

position of first element in the array

current pos in type_str

type_pos can be either an insertion point for or an expected next type

where to write typecodes (or read type expectations)

class-specific data

next position to write

where to write values