Matching axes

We should allow two (or more) axes to not just share a scaling, but actually force precisely equal range. Use case is plots like this one:

This came up in https://github.com/plotly/plotly.js/issues/272#issuecomment-287043579 but was not addressed in #1522 - opening this as a new issue so we don’t forget about it.

[alexcjohnson]

matching axes of the same letter (i.e. ‘x’ or ‘y’) would suffice for the first iteration

if that’s a lot easier, OK, it won’t cause any API problems to enable it later. But I kind of don’t think it’ll be that much harder to do x/y matching since we already have that for scale constraints. And it would be really nice to use with splom - it would mean that if you zoom on one off-diagonal subplot, not only would the whole row & column through that subplot zoom but the symmetric row & column would also zoom to match.

[alexcjohnson]

How would this proposal be different than having ax.matches and ax.scaleanchor (under constrain: ‘domain’) set.

Only that I didn’t want to allow scaleanchor at all when you already have matches. I guess it may be clearer that way, as it means “range matches AND scale matches”… just seems weird as the only allowed values of scaleanchor would be ’x’ or nothing.

I’m not sure who should “win out”

Agreed, that would be meaningless.