https://conwaylife.com/wiki/Run_Length_Encoded
e.g.: https://github.com/nhoffmann/life/tree/master/rle https://github.com/sachaos/go-life/tree/master/format/rle
rle files: https://catagolue.hatsya.com/object/xq2_32mmgozg0igke72z1n2q1z0qgm1z31i2bsogzggqq261z1/b3s23 https://copy.sh/life/examples/
