Build by Rules

one: RBB=GGR changes one random match per step. all: changes every match that does not overlap, at once. prl p=0.3: changes each match with probability p. markov: with indented lines underneath tries them in order each step and uses the first that can act.

Rows of a picture are separated by /. * on the left matches anything; on the right it leaves the cell alone. sym=x allows mirror images only, sym=none only the rule as written; the default allows all turns and mirrors. steps=N caps a line. ~3 after a rule makes it three times as likely in a one line. # starts a comment.

start size=48 fill=B origin=W@center ground=N sets the empty grid. Origin may be @center or @bottom.