President Donald Trump questioned former President Joe Biden’s autopen-signed pardons, calling them “void," as experts weigh whether courts could rule on the validity of presidential clemency.

The use of the autopen, a device that reproduces signatures and is ubiquitous in government and business, is ordinarily uncontroversial. There is no power to undo a pardon in the Constitution or case law.

Donald Trump says Joe Biden's last-minutes pardons via autopen are null and void. But what is an autopen? And what does it mean for pardons?