`\\[ibuffer-mark-by-mode-regexp]' - Mark buffers by their major mode, using a regexp.
`\\[ibuffer-mark-by-file-name-regexp]' - Mark buffers by their filename, using a regexp.
`\\[ibuffer-mark-by-content-regexp]' - Mark buffers by their content, using a regexp.
`\\[ibuffer-mark-by-mode-regexp]' - Mark buffers by their major mode, using a regexp.
`\\[ibuffer-mark-by-file-name-regexp]' - Mark buffers by their filename, using a regexp.
`\\[ibuffer-mark-by-content-regexp]' - Mark buffers by their content, using a regexp.