TODO

New type pattern
Box, Arc, Rc, Vec, Option
- FromIterator cannot be implemented for Option<T> so #[knuffel(child, unwrap(_))] approach can't be used
Semantic difference between structs with and without fields (unit/tuple structs)
- Enum variants with single Decode element without attribute vs variants with single scalar element with attribute
- Do we need arguments/properties/children? Is there a case where a type can be used for both patterns?
- Lack of documentation about tuple structs
#[knuffel(child, unwrap(children(name)))] plugins: Vec<String> instead of Vec<Plugin> doesn't work?
Are there any possible uses of generics?

Cheat Sheet

definition	attribute (`#[knuffel(_)]`)				field/variant (`T` : `DecodeScalar`, `U` : `Decode`)	examples of X	input → output	reference
definition	field mode	name	decode mode	unwrap	field/variant (`T` : `DecodeScalar`, `U` : `Decode`)	examples of X	input → output	doc	impl
unit struct	-				X	-	- → `Default::default()`
struct	-				X	-	- → `Default::default()`
	`argument`	-	-	-	`T`	-
					`bool` TODO
					`Option<T>`
			`str`		X : `FromStr`	`SocketAddr`, `PathBuf`
			`bytes`		X : `TryInto<Vec<u8>>`	`Vec<u8>`
	`arguments`	-	-	-	X : `FromIterator<T>`	`Vec<T>`
	`property`	-	-	-	`T`	-
		-	-		`Option<T>`	-
		name	-		`T`	-
	`properties`	-	-	-	X : `FromIterator<(S, T)>` where `S` : `FromStr`	`HashMap<String, T>`
	`child`	-	-	-	`bool`	-	`field`/ → `true`/`false`	Children.Boolean Child Fields
					`Option<U>`	-
					`U` (struct)	-
				`argument`	`T`
				`property`	`T`
				`child`	`T`
	`children`	-	-	-	`Vec<U>` (enum)	-
	`children`	name	-	-	`Vec<U>` (struct)	-
enum	-				-	-	Single struct.	Enum
	`argument`
	`arguments`
	`property`
	`properties`
	`child`
	`children`

KDL's Features/Principles

What is the KDL's culmination as a format or language?

All nodes have a name

Nodes of the same type can appear at different times

By this, name value construct has different semantics from name=value one. The former is cumulative, enumerating. The latter is overriding, idempotent.
This is a very important –– even departing –– point as
- if we let the former have nesting mode (value = { name value }), we get KDL, and
- if we let the latter have nesting mode (value = { name=value }), we get TOML in place.
Entry/occurrence of nodes are not arbitrary but predicted by parent nodes.

Line breaks are delimiters, no colons