Emily KL

> Another thing, is if someone does `raise PreventUpdate` in a legit callback return, this flags as an error and would trigger the `on_error`, is this correct? Just tried this...

@T4rk1n See my comments regarding outputs from the error handler. Otherwise LGTM.

We shouldn't recommend `pip install plotly.express` , I believe it only exists for backwards compatibility and it's confusing to have multiple install paths. If we want to have a one-liner...

IMO the naming should be `plotly[pandas]` rather than `plotly[express]` -- much more clear what it's actually doing. I'm in favor of this change, but let's not merge it right away....

@marthacryan `pip install plotly[pandas]` would be roughly equivalent to `pip install plotly && pip install pandas` I believe.

> @emilykl Do you think that the height of subtitle should push the margins? In your example if I set `subtitle.text: '1st2nd3rd4th'` the subtitle would go over the cartesian subplot...

> This is quite minor. But I noticed when `config.editable` is set to true and having an empty subtitle I get a **black** subtitle instead of gray on `Click to...

Yes I'm getting those same failures locally too @archmoj . I'm having trouble figuring out how to debug, please let me know if you have any suggestions!

@archmoj Good catch. Overall the behavior on `master` is better, I agree. Although the location of the placeholder (above the colorbar rather than overlapping it) is better on this branch....

@archmoj I believe the above issue with the colorbar title is fixed. (Colorbar tests are passing on my machine; we will see if they pass in the CI.) The issue...