Annotations referenced to the y-axis are in the wrong place, for log-scales

[RichardNeill]

If I have:

• a point at value y=3
• an annotation at value y=3, with yref=y
  then the annotation is attached to the point, as expected.

But If I then make the y-axis have type=log, then the annotation comes adrift from the point.
https://codepen.io/RichardNeill/pen/dyreyMG

What's happening is that the annotation is being drawn in linear units - it isn't truly referenced to the yaxis, because if you read across, the y-value for the annotation is 10E3, not 3.

This might be a problem to fix, given that it would be backward-incompatible - see #420.
If so, please at least consider warning about this issue at: https://plotly.com/javascript/text-and-annotations/
A suitable message might be:

Note, for backward compatibility, annotations are drawn in linear units. So if your axis-type is log, remember to use:
yref:y, y:Math.log10(your_y_value)

Thanks :-)

[alexcjohnson]

You're exactly right @RichardNeill - an unfortunate decision very early in the history of plotly.js 😅

@LiamConnors thoughts on how best to warn people about this? We do already mention this in the description for x and y, but you'll only see that if you look carefully at the reference for these attributes:

plotly.js/src/components/annotations/attributes.js

Lines 366 to 367 in 5272c38

	'If the axis `type` is *log*, then you must take the',
	'log of your desired range.',

[LiamConnors]

Yeah, we could add an example to the annotations page of what that would look like with a log axis. Will add it in.

[LiamConnors]

Examples are live now at https://plotly.com/javascript/text-and-annotations/#annotations-with-log-axes
https://plotly.com/python/text-and-annotations/#text-annotations-with-log-axes