The word 'Christ' was sometimes indicated by a Greek letter chi (which looks like an X) sometimes followed by a Greek letter rho (which looks a bit like a p) or by a combination of the two letters, the chi-rho symbol. Thus what looks like X or Xp can be shorthand for Christ. The most familiar result is the use of Xmas to mean Christmas. Here are some other examples which you may encounter in parish registers etc.: Xenings / Xened = Christenings / Christened Xian or Xtian = Christian Xopher or Xpofer = Christopher
Here's an example of a 'Xopher' from the parish register of St Botolph, Aldgate, in January 1588/9: Mawdelen bushopp dawghter unto [Christ]opher bushopp a garden[er] Was baptized the 5 daie of January Anno p[re]dicto The Ancestry transcriber has transcribed this as Xopher so it would not come up if you searched for Christopher.
Presumably Ancestry's transcribing minions are told to transcribe "as is" - as indeed are those of us in the Cornwall OPC transcribers. Xopher is what I would transcribe it as - and assume that a researcher would search using Chris to cover Christopher, Chrisr. etc and Xopher should also be tried. Quite a common abbreviation in the late 1500s and early 1600s I find.
I agree absolutely that good transcribers should transcribe what is there and not what they think ought to be there. My caption to the photograph is not an example of good practice: I should have put 'xopher [Christopher]' instead of '[Christ]opher' but was too late to edit it. I am not trying to suggest that Xopher should be transcribed as Christopher, just trying to make more people aware that if they are looking for a Christopher they should also try searching for Xopher.
I was lucky enough to pick that Xopher enlightenment up some years ago when I purchased a booklet from the Essex Family History Society entitled "Simple Latin for Family Historians", although it doesn't mention Xmas for Christmas. It did come as a bit of a shock though when I found out from PRs that Xmas is not the modern shortening of Christmas that I had always thought it to be.
Ditto With shame, I must admit that I too thought it was just a lazy modern way of writing Christmas - but then I did Latin at school, not Greek It doesn't stop me loathing seeing Christmas shortened like that, though, but I suppose I will have to try to be more tolerant and consider that all the shorthanders and texters must be well-versed in Ancient Greek. Somehow, I don't think so