Control on-board LED? Zero 3E/W

I came across the following…
https://wiki.radxa.com/Rock/LED

And specific to my zero 3E I know the list of possible triggers via…

# cat /sys/class/leds/board-led/trigger

But one, ‘pattern’ I have yet to find any information about? Heatbeat, default-on, timer, etc., make sense. In that I am sure ‘timer’ has a way to set the time between led state change? Default seems to be, on 1 second, off 1 second. This variant of ‘pattern’? So can one set a pattern then trigger it right?

I did not see any obvious way to set the timer or the pattern if that is possible?

# ls -l /sys/class/leds/board-led/
total 0
-rw-r--r-- 1 root root 4096 Aug 16 05:33 brightness
lrwxrwxrwx 1 root root    0 Aug 16 05:33 device -> ../../../gpio-leds
-rw-r--r-- 1 root root 4096 Aug 16 05:33 invert
-r--r--r-- 1 root root 4096 Aug 16 05:33 max_brightness
drwxr-xr-x 2 root root    0 Aug 16 05:33 power
lrwxrwxrwx 1 root root    0 Jan  1  1970 subsystem -> ../../../../../class/leds
-rw-r--r-- 1 root root    0 Aug 16 05:33 trigger
-rw-r--r-- 1 root root 4096 Jan  1  1970 uevent

Oh, and what is the scale for brightness? 0-255 or some thing like that? Given max_brightness is 255. But I guess the Zero does not really have brightness level control? I tried setting it to 0, turned off, set to anything not 0, just seems to enable led, but no real change in ‘brightness’ per se, that I can see?

One more question, for disk related triggers? I take it, which ever device, microSD or eMMC, that is the boot device, is applicable, right? But what is nand-disk versus ‘disk*’ then?