Graftroot: Private and efficient surrogate scripts under the taproot assumption

On February 22nd, 2018, Ryan Grant posted on the Bitcoin-dev list regarding a suggestion made by Jeremy to improve the utility of a construction by introducing functionality that makes a script invalid after a certain time. The thread was tagged with "nExpiryTime" and users were encouraged to search the archives for more information. The term "fill-or-kill transaction" was also mentioned in a past discussion on the same list in September 2015. The post was signed off by Sjors.