Toggleable not working on field "fieldset"

[According to the docs](https://learn.getgrav.org/17/forms/blueprints/fields-available#fieldset-field), the field `fieldset` allows the common attribute `toggleable`. This took me by surprise, but would actually be ideal for my case.

However the setting does not seem to work. If I add it to my fieldset nothing changes. There is no checkbox to activate or deactivate the fieldset. Is toggleable actually implemented for fieldsets, or is this a mistake in the docs?

I think this would be a great option, because it would be an easy option to activate or deactivate a whole bunch of correlating settings.