In this snippet of -Xlog:help output:

 -Xlog:gc+ref=debug
         Log messages tagged with both 'gc' and 'ref' tags, using 'debug' level, to stdout, with default decorations.
         (Messages tagged only with one of the two tags will not be logged.)

The "using 'debug' level" part is accurate only if there are no
calls to log_info(gc, ref)("...") in the system. David Holmes
suggested that this wording might be better:

    "using 'debug' level" => "using up to 'debug' level"

and I agree that would be a more inclusive statement
since we could have output at the "error", "warning",
"info" and "debug" levels in the above example.