Perhaps I am overlooking this, but I think it would be useful if the starting node could be specified in some way, perhaps via XPath. While trying to implement an RSS feed, I found that I either have to implement the parent node to get to the child nodes I am interested in or write my own init(from decoder: Decoder).

For example:

<?xml version="1.0"?>
<rss version="2.0">
  <channel>
    <title>Title</title>
…
  </channel>
</rss>

To get to the title node, I need to implement a type for the channel node as well:

struct RSSFeed: Decodable {
  let channel: Channel

  struct Channel: Decodable {
    let title: String
  }
}