enums are not considered a valid parameter to `d.arg()`

[nogweii]

I'm using the docsonnet binary, and it's complaining about the parameter:

$ docsonnet -J $(pwd)/lib -J $(pwd)/vendor lib/kube-things.libsonnet -o docs
Extracting from Jsonnet
Extracting: RUNTIME ERROR: function has no parameter enums
	lib/kube-things/secrets.libsonnet:55:7-109	thunk from <thunk from <object <anonymous>>>
	Array element 2	
	Field "args"	
	Field "function"	
	Field "#withField"	
	Field "secretGen"	
	During manifestation

Where lib/ and vendor/ are folders from my tanka project, and lib/kube-things/secrets.libsonnet looks sorta like (snipped):

local d = import 'github.com/jsonnet-libs/docsonnet/doc-util/main.libsonnet';

{
  '#secretGen': d.obj("Helpful functions wrapping around Mittwald's Secret Generator operator"),
  secretGen: {
    '#randomPasswordSecret': d.fn('Create a StringSecret (a custom resource) to generate a normal Secret with random content', [
      d.arg('name', d.T.string),
      d.arg('fieldName', d.T.string, default='password'),
      d.arg('length', d.T.number, default=48),
      d.arg('encoding', d.T.string, default='base64', enums=['base64', 'base64url', 'base32', 'hex', 'raw']),
      d.arg('data', d.T.object, default={}),
    ]),
    randomPasswordSecret(name, fieldName='password', length=48, encoding='base64', data={}):: {
      apiVersion: 'secretgenerator.mittwald.de/v1alpha1',
      kind: 'StringSecret',
      metadata: {
        name: name,
      },
      spec: {
        [if data != {} then 'data']: data,
        fields: [
          {
            fieldName: fieldName,
            length: std.toString(length),
            encoding: encoding,
          },
        ],
      },
    },
  },
},

[nogweii]

Looking into the code, I think it's because the go code doesn't have Enums as part of the Argument model object? Do I understand the codebase correctly?

https://github.com/jsonnet-libs/docsonnet/blob/master/pkg/docsonnet/model.go#L32-L37