Button purpose property

[mhsmith]

Invent buttons have a purpose property which currently accepts the following options:

• Default (i.e. no special style – this should probably be renamed to "normal" or something to avoid confusion with the concept of a "default button")
• Primary
• Secondary
• Success
• Warning
• Danger

This is based on the list from PaperCSS, but Invent also intends to support other style frameworks, so the list is open to change.

Some of Toga's existing platforms support a similar concept, e.g. Apple calls it a "role".

The name of this property is TBD – "class" might be a more generic name, but it's a reserved word in Python.

[freakboy3742]

A big +1 to this one. One of the main reasons we support background_color on buttons is to satisfy the use case of "making a button stand out"; but most platforms have the ability to make "warning" and "error" buttons that entail a specific platform appearance. "Purpose" is a much better to approach that problem.

By way of naming - a quick survey of existing API naming for this idea:

• Invent: purpose
• iOS/macOS: role
• paperCSS: class (leaning directly on CSS)
• bootstrap: class (again, leaning on CSS)
• Shoelace: variant
• Textual: variant

I couldn't find any native concept of this idea for GTK, Winforms, WinUI3 or Android/Material3.

This is (almost literally) a bike shed, and there's no clearly established precedent for the feature, so IMHO any of the names purpose, role or variant are perfectly cromulent.