confusing API for heatmap legend

When trying to customize the legend for a heatmap I would expect that to be done through the layout similar to other trace types.

plot_ly(
  z = volcano, 
  type = "heatmap",
) %>%
  layout(
    legend = list(
      title = list(
        text = "custom title"
      )
    )
  )

After digging around for a while and examining the output of plotly_build() %>% plotly_json() I found that this is done through the top level colorbar instead.

plot_ly(
  z = volcano, 
  type = "heatmap",
  colorbar = list(
    title = "custom title"
  )
) 

I would say that if the interface for this needs to be different than for other traces, that should be documented on the heatmap page. Even better may be to standardize the approach so that users always know to go to layout for this type of thing.

I'm also curious why colorbar title is shown as a deprecated attribute from schema().

Start with the R heatmap page linked in the issue and inspect the documented examples alongside the plotly_build() and plotly_json() output described there. Document that heatmap legend customization uses the top-level colorbar, including the schema() deprecation detail; completion means a newcomer can find and follow the documented interface.