cvs-mode-marked is a compiled Lisp function in `pcvs.el'.

(cvs-mode-marked FILTER &optional CMD &key READ-ONLY ONE FILE NOQUERY)

Get the list of marked FIS.
CMD is used to determine whether to use the marks or not.
Only files for which FILTER is applicable are returned.
If READ-ONLY is non-nil, the current toggling is left intact.
If ONE is non-nil, marks are ignored and a single FI is returned.
If FILE is non-nil, directory entries won't be selected.