How do I apply keywords for "metadata.content-format" correctly with "custom" mode?

[Aidanjosiah02]

The title basically says it all. This is probably due to not understanding how to properly format JSON fields, however, the documentation is lacking in some areas (though it is a lot of work so I don't blame the writers). I figure I need to use the "custom" mode, referenced here (https://github.com/mikf/gallery-dl/blob/master/docs/configuration.rst#metadatamode), and add keywords (such as "author[username]", "date", etc.) in the manner referenced here (https://github.com/mikf/gallery-dl/blob/master/docs/configuration.rst#metadatacontent-format). But the problem is, the example doesn't include in what way relative to the "mode": "custom" string I need to add my keywords. Please see below for the relevant section of my config file.
So, how do I do this?

{
    "extractor":
    {
        "base-directory": "./gallery-dl/",
        "parent-directory": false,
        "postprocessors": [
            {"name": "metadata", "mode": "json"},
            {"name": "metadata", "mode": "custom"}
          ],

[Aidanjosiah02]

I'm so stupid. I have to use "content-format": [{keyword}, etc.]. I can't believe I didn't think of this for SIX hours. Replaced row 6 above with:
{"name": "metadata", "event": "post", "mode": "custom", "content-format": ["{author[username]}", "{date}"]}
and it gave me:
"Aquilapse
2016-03-24 16:24:23"
which is what I'm looking for.