The wk package doesn't operate on CRS objects, but does propagate them through subsetting and concatenation. A CRS object can be any R object, and x can be any object whose 'crs' attribute carries a CRS. These functions are S3 generics to keep them from being used on objects that do not use this system of CRS propagation.
wk_crs(x)
# S3 method for class 'wk_vctr'
wk_crs(x)
# S3 method for class 'wk_rcrd'
wk_crs(x)
wk_crs(x) <- value
wk_set_crs(x, crs)
wk_crs_output(...)
wk_is_geodesic_output(...)