This is rather lenient. There's not anything wrong with that (although perhaps it should be noted for people that will use it without looking at the code), but it's the main reason this can be so small. Using their demo in the readme:

    {"x",10eee"y"22:5,{[:::,,}]"w"7"h"33
    rect: { 10, 22, 7, 33 }

Parser, implies the input is assumed to be valid, validating is a whole other problem not covered by this library.

I don’t know what else you call a library that just extracts data.

so it is wrong?