In the Python community, agreement with a proposed change (“this is a good idea”) is indicated by +1, disagreement (“this is a bad idea”) is indicated by -1, and mostly indifference leaning slightly for or against (as in “I (dis)approve but don’t really care”) is indicated by +0 or -0. My guess is that -0.small is intended to mean something like “I slightly disapprove but this is utterly insignificant”.

Edit: much more amusing is Antoine’s comment “[...] Otherwise +11j from me”