ISETH.sol,which can be found here:
SETH.solcontract has a payable function called
upgradeByETH()which takes no parameters but is expected to receive some nonzero
msg.valuewhen it's called. This function will mint a number of native asset super tokens that is equivalent to the total amount of the
msg.valuesent along with the function call. Calling
downgradeToETH()and passing in the amount of the native asset super token you'd like to downgrade will burn native asset super tokens and send you back that amount of the underlying asset.