Golly prefers to store patterns and pattern fragments in a simple concise textual format we call "Extended RLE" (it's a modified version of the RLE format created by Dave Buckingham). The data is run-length encoded which works well for sparse patterns while still being easy to interpret (either by a machine or by a person). The format permits retention of the most critical data:
The cell configuration; ie. which cells have what values.
The transition rule to be applied.
Any comments or description.