list-command-history-filter

list-command-history-filter is a variable defined in `chistory.el'.
Its value is

default-command-history-filter

Documentation:
Predicate to test which commands should be excluded from the history listing.
If non-nil, should be the name of a function of one argument.
It is passed each element of the command history when
M-x list-command-history is called. If the filter returns non-nil for
some element, that element is excluded from the history listing. The
default filter removes commands associated with the command-history.