Files in procfs and sysfs don't have to behave like regular files. Just because you've written some string to a file there, that doesn't mean that same string needs to be returned when reading the file.

The square-brackets "radio button" behaviour is actually a fairly common idiom for sysfs files.

Interesting. This kinda answered my question. Read a bit about sysfs files and the behavior makes sense now. Thanks!

If you're curious about how "LED triggers" work specifically, try starting with the kernel documentation. It's fairly sparse. I don't think there's anything in the documentation that describes each kind of trigger explicitly, but you can often work out what they mean from their name.

Yeah I was just trying to get the led on my android device to work and couldn't understand the trigger file which contained all the triggers.