mark commands and (vmark)

mark: Put a special flag on the current buffer.

Marked buffers are hilighted with a star on the upper left corner of the plots (both in (normal) plots of single data sets and when you're seeing the stack).

unmark: Remove the flag on the current buffer

vmark: Plot (overlay) all marked buffers and the current buffer. There are screen shots there.

(un)markall: Also provided are markall and unmarkall to mark all buffers or remove all flags.

(un)markN: Instead of (un)marking the current buffer, you can (un)mark any buffer at any time using e.g. mark9 to mark the 9th buffer, or unmark16 to remove the flag on the 16th buffer. This can be useful while you're seeing the stack.

There is a default message "ERROR: no action taken" if you try to (un)mark an empty or already (un)marked buffer.