Extend multicategory axes to more than 2 levels

This is a request to add nested categorical axes. These are often used in "variability charts", examples of which can be seen here.

There's a few ways this could be implemented in practice. Rather than passing an array of values for y the user could pass an object like:

{
  "popcorn": ["gourmet", "gourmet", "plain", ...]
  "batch": ["large", "small", "large", ...]
  ...
}

or simply pass a category name / number (1 or "gourmet-large-little") and pass the nesting information for the axis in the layout section.

(I was surprised not to find an open issue for this -- it's possible that there is one but I didn't search using the right terms).

Edit: There is some limited support for this as shown here but it involves hacking the axis together by hand and would be difficult to use in an automated manner.

Comece revisando o suporte limitado existente a eixos de subcategorias descrito na documentação vinculada sobre eixos do Plotly e nos exemplos de gráficos de variabilidade. Esclareça se a API deve aceitar arrays de categorias aninhados ou metadados de aninhamento no nível do layout e, em seguida, rastreie o comportamento atual do eixo multicategory. O trabalho estará concluído quando os eixos categóricos aninhados funcionarem automaticamente sem a construção manual dos eixos.