what block layer parameter events_dfl_poll_msecs used for?

hi all: in block layer, there is one paramter like below: /sys/module/block/parameters/events_dfl_poll_msecs when I search the usage in Document, I cannot find anything. from the src, it seems firing media_chage at a fixed interval. is my guess correct? and is there any furhter debug option I can open to make sure block layer did firing those events to lower device? appreciate your kind help in advance,