The number of ON bits in bit string replaces top. BTS Converts top to string. It is actually a byte-encoded bitstring. BTI Convert top to integer. This is only valid for bitstrings which have less than 32 bits.
Branches use a relative offset which is encoded in the next two bytes of the bytecode.
Pop the top. Pop the top. BRU Branch unconditionally. A total of 10 files may be open at one time. Pops these three elements and pushed file index.