docs: function parse_ImData(blob, length, opts) {
  	var tgt = blob.l + length;
  	var cf = blob.read_shift(2);
  	var env = blob.read_shift(2);
  	var lcb = blob.read_shift(4);
  	var o = {fmt:cf, env:env, len:lcb, data:blob.slice(blob.l,blob.l+lcb)};
  	blob.l += lcb;
  	return o;
  }