While studying the jelpi.p8 file I noticed that its using some things that aren't documented in the manual (pico-8.txt) file so I figured I'd post it here.

Missing math function:
sgn(x) returns -1, 0, or 1 based on the sign of the input value, currently passing in 0 returns 1 (maybe a bug)

Missing optional properties:
spr(n, x, y, [w, y, [flip]] the normal draw sprite function can also take the optional flip bool (not documented)

I'm also pretty sure that the optional flip parameter isn't working with the sspr function even though it is in the documentation.

Thanks for posting this.