The package takes control of the six TeX token registers
\everypar, \everymath, \everydisplay, \everyhbox, \everyvbox
and \everycr. Real hooks for each of the registers may be
installed using a stack like interface. For backwards
compatibility, each of the \everyX token lists can be set
without interfering with the hooks.

Homepage:
https://ctan.org/pkg/everyhook
