The rule is defined by a four-digit number,
where each digit must be from 0 to 7.
Digit 0-3 means rotation by 0,90,180,270 degrees.
Digit 4-7 means vertical flip followed by rotation of 0,90,180,270 degrees.
For each iteration, four copies are made and transformed as specified,
then shrunk by half and moved to four corners. The four digits
correspond to transformations on upper-left, upper-right, lower-left and
lower right, respectively.
The resulting rule is also shown graphically above.
There is a total of 8^4=4096 different rules, although some of them
produce the same patterns.
Hints: Try using arrow keys to slide. Press "enter" after you
specify a rule.
Let me know (firstname.lastname@example.org) if you find some other cool patterns that you'd like to add
to the list.