I've seen an HTTP header called X-iinfo. Her are some examples:
X-Iinfo: 5-17009424-17011001 PNNN RT(1388193526625 4677) q(0 0 0 -1) r(1 1) U10000
X-Iinfo:4-13055499-13055501 NNNN CT(182 -1 0) RT(1388193578304 0) q(0 0 1 4) r(6 6) U1
Parts of them (but not all) seem to change on refresh.
What is this header?