Bip16 defines whether the bip16 threshold has passed and thus pay-to-script hash transactions will be fully validated.

DiscourageUpgradableNops defines whether to verify that NOP1 through NOP10 are reserved for future soft-fork upgrades.

EnableSighashForkID defined that signature scripts have forkid enabled.

StrictMultiSig defines whether to verify the stack item used by CHECKMULTISIG is zero length.

UTXOAfterGenesis defines that the utxo was created after genesis.

VerifyBip143SigHash defines that signature hashes should be calculated using the bip0143 signature hashing algorithm.

VerifyCheckLockTimeVerify defines whether to verify that a transaction output is spendable based on the locktime.

VerifyCheckSequenceVerify defines whether to allow execution pathways of a script to be restricted based on the age of the output being spent.

VerifyCleanStack defines that the stack must contain only one stack element after evaluation and that the element must be true if interpreted as a boolean.

VerifyDERSignatures defines that signatures are required to comply with the DER format.

VerifyLowS defines that signatures are required to comply with the DER format and whose S value is <= order / 2.

VerifyMinimalData defines that signatures must use the smallest push operator.

VerifyMinimalIf defines the enforcement of any conditional statement using the minimum required data.

VerifyNullFail defines that signatures must be empty if a CHECKSIG or CHECKMULTISIG operation fails.

VerifySigPushOnly defines that signature scripts must contain only pushed data.

VerifyStrictEncoding defines that signature scripts and public keys must follow the strict encoding requirements.

Flag is a bitmask defining additional operations or tests that will be done when executing a script pair.