Feature request: passing lists in [extra]

[ghost]

I like something like this:

[group.activities]
paths=["activities"]

[group.activities.note]
filename = "{{id}}-{{slug title}}"
extension = "md"
template="activities.md"

[group.activities.extra]
author = "Me"
keywords = ["activities", "really stuff"]

and in template:

keywords: {{group.extra keywords]]

But it gives me an error

[mickael-menu]

It's not supported, extra can only contain strings at the moment.