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stat(4) -- clipboard; after user pressed ctrl-v
stat([16..19]) -- index of playing sfx on channels [0..3]
stat([20..23]) -- note number (0..31) on channels [0..3]
stat(30) -- keyboard key hit; see "peek / poke" tab
stat(31) -- keyboard character; see "peek / poke" tab
stat(32) -- mouse x coord; see "peek / poke" tab
stat(33) -- mouse y coord; see "peek / poke" tab
stat(34) -- mouse button bitmask; see "peek / poke" tab

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stat(0) --[[ Memory Usage
The number returned is a value in Kilobytes, with 1 representing 1024 bytes.
Any decimal value returned is accurate, for example, 1.875 is equivalent to 1920 bytes.
This value accounts for ANY & ALL data used in the Lua code, including variables and tables, etc.
Thus, the maxiumum amount this can return is 2048, ie, 2 Megabytes, the total amount of memory alloted to Lua.
This value does NOT include any peekable/pokeable RAM, ie, graphical/video, nor does it include the cart ROM.
]]--
stat(1) --[[ Total CPU Usage
Initializes at 0 from the first _update call after the most recent _draw call.
The value will increment steadily towards 1 as the next frame approaches.
Ultimately, if the _update function is used, a value of 1 would represent 1/30th of a second having elapsed.
If instead the _update60 function is used, a value of 1 would represent 1/60th of a second instead.
Any time this returns a value exceeding 1 is an indication that the current cart is beyond the processing power it
is allotted for that frame. This means that frames will likely be dropped to compensate for the slow down.
]]--
stat(2) --[[ System CPU Usage
This value represents the the range/behavior seen in stat(1)
The difference between the two is that this value will only increase when PICO-8 is processing unseen code.
For example, if the screen was cleared 70 times in a step, stat(2) would return a value > 1. 
That's because the cls() function is a system call, but if the frame was spent calculating PI,
stat(2) wouldn't rise, as such calculations are not system calls.
]]--