Module CommaDelimitedList parameters

The [modules documentation](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/modules.html) says,
> Module parameters don't support Type or Constraint enforcement.

Does that mean that modules can't support CommaDelimitedList parameters?

We have a module fragment:
```
---
Parameters:
Plan:
Type: String
Role:
Type: String
Arns:
Type: CommaDelimitedList

Resources:
Selection:
Type: AWS::Backup::BackupSelection
Properties:
BackupPlanId: !Ref Plan
BackupSelections:
SelectionName: "For demonstration only"
IamRoleArn: !Ref Role
Resources: !Ref Arns
```

And we use it in a template:
```
Resources:
Volume:
Type: AWS::EC2::Volume
# etc...

Backup:
Type: Hiya::Backup::Assignment::MODULE
Properties:
Plan: !Ref SomeBackupPlan
Role: !Ref SomeRole
Arns: !Ref Volume
```

When we create a stack from that template, CloudFormation reports the error:
```
{
"StackId": "arn:aws:cloudformation:us-west-2:nnnnnnnnnnnn:stack/a-stack/bbbbbbbb-bbbb-bbbb-bbbb-bbbbbbbbbbbb",
"EventId": "BackupSelection-CREATE_FAILED-2021-04-06T19:06:59.117Z",
"StackName": "a-stack",
"LogicalResourceId": "BackupSelection",
"PhysicalResourceId": "",
"ResourceType": "AWS::Backup::BackupSelection",
"Timestamp": "2021-04-06T19:06:59.117000+00:00",
"ResourceStatus": "CREATE_FAILED",
"ResourceStatusReason": "Properties validation failed for resource BackupSelection with message:\n#/BackupSelection/Resources: expected type: JSONArray, found: String",
"ResourceProperties": "{\"BackupSelection\":{\"SelectionName\":\"For demonstration only\",\"IamRoleArn\":\"arn:aws:iam::nnnnnnnnnnnn:role/a-stack-BackupRole-MMMMMMMMMMMMM\",\"Resources\":\"vol-vvvvvvvvvvvvvvvvv\"},\"BackupPlanId\":\"aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaaa\"}"
},
```

When we force the argument to be a list, we get a different error:

```
Backup:
Type: Hiya::Backup::Assignment::MODULE
Properties:
Role: !Ref SomeRole
Plan: !Ref SomeBackupPlan
Arns: [ !Ref Volume ]
```

```
"StatusReason": "Template format error: Unresolved resource dependencies [BackupVolume] in the Resources block of the template"
```

We think we can work around this error ourselves by manually packing the arguments in the stack template...
```
Backup:
Type: Hiya::Backup::Assignment::MODULE
Properties:
Role: !Ref SomeRole
Plan: !Ref SomeBackupPlan
Arns: !Join [ ",", !Ref Volume ]
```

... and unpacking them at the underlying resource:
```
Selection:
Type: AWS::Backup::BackupSelection
Properties:
BackupPlanId: !Ref Plan
BackupSelections:
SelectionName: "For demonstration only"
IamRoleArn: !Ref Role
Resources: !Split [",", !Ref Arns]
```

Are modules unable to handle native list parameters?