Introduced by Kapoutsis 2009, as a straightforward example of a problem
in 22D\2D. (The original definition allowed arbitrarily long instances, but
this is not essential in this context.)
The name “long length” is suggested by this site. huh?
See iterated long length for the variant where the length must be a multiple of $2^h$,
and length for the variant where the length must be $h$.