Using the size to trigger compression vs no-op is clever, but doesn't help when you have different compression methods that you want to use. For example, you b

Using the size to trigger compression vs no-op is clever, but doesn't help when you have different compression methods that you want to use. For example, you be using this as an archive format for a game, and you may want to store the texture data using a different compression method than the ai scripts or the audio data. At that point, you definitely need another piece of data to clue you in. A tag field is useful then, though I've also seen filename/file extension-based methods as well.