Aside from the previously mentioned OP_CHECKSIGALT and OP_CHECKSIGALTVERIFY, other modifications to Bitcoin scripting have been made. A version byte has been added to output scripts to enable simple soft forking to new scripting languages, as first suggested by Wuille1. All math and logic related OP codes have been re-enabled and now operate on int32 registers. Various byte string manipulation OP codes have also been implemented and re-enabled. The remaining unused Bitcoin OP codes have been repurposed for future soft forks. Some longstanding bugs in the Bitcoin scripting language have been also been fixed2 3.
Franco P. Understanding Bitoin, 6.3: Multisignature (M-of-N) Transactions. ↩