These dots are for future extensions and must be empty.
null.ok
Is NULL permitted?
contains
Character vector of names that must be bound in the
environment. Applies to chk_environment().
attr.ok
Which attributes x may carry beyond those intrinsic to its
type: a character vector of permitted attribute names, FALSE for none at
all, or TRUE for any. Applies to chk_list().
length
Permitted length. NULL for any length, a scalar for one
exact length, or a vector whose first and last elements give the minimum
and the maximum. Neither may be negative, and NA at an end, or Inf as
the maximum, means no bound there.
See Also
chk_atomic for the scalar and vector types, and chk_other for
classes, conditions, and the rlang aliases.