Update properties page with recent Var changes

ReadMe.md

@@ -1,19 +1,19 @@
 # The godot-rust book
 
-This book is a user guide for **godot-rust**, the Rust bindings to Godot 4.
-It covers a large part of the concepts and complements [the API docs][gdext-docs].
-There is also [gdnative-book] for Godot 3.
+This book is a user guide for **godot-rust**, the Rust bindings to Godot 4.[^gdnative-book]  
+It covers a large part of the concepts and complements [the API docs][api-docs].
 
 > [!Tip]
 > The book is deployed at **[godot-rust.github.io/book][book-web]**.
 
 
 ## Local setup
 
-The book is built with [mdBook] and the plugins [mdbook-toc] and [mdbook-admonish]. To install them and build the book locally, you can run:
+The book is built with [mdBook] and the plugins [mdbook-toc] and [mdbook-admonish].[^mdbook]  
+To install them and build the book locally, you can run:
 
 ```bash
-cargo install mdbook mdbook-toc mdbook-admonish
+cargo install mdbook@^0.4 mdbook-toc@^0.14 mdbook-admonish@1.18.0
 mdbook build
 ```
 
@@ -51,7 +51,7 @@ oxipng --strip safe --alpha -r src
 ## Contributing
 
 This repository is for documentation only. For changes in the library itself, please open pull requests and issues in the [main repo][gdext],
-and read the [contributing guidelines][gdext-contribute].
+and read the [contributing guidelines][contribute].
 
 
 ## License
@@ -60,8 +60,8 @@ Like godot-rust itself, the godot-rust book is licensed under [MPL 2.0][mpl].
 
 [book-web]: https://godot-rust.github.io/book
 [gdext]: https://github.com/godot-rust/gdext
-[gdext-docs]: https://godot-rust.github.io/docs/gdext/master/godot
-[gdext-contribute]: https://github.com/godot-rust/gdext/blob/master/Contributing.md
+[api-docs]: https://godot-rust.github.io/docs/gdext/master/godot
+[contribute]: https://github.com/godot-rust/gdext/blob/master/Contributing.md
 [gdnative-book]: https://github.com/godot-rust/gdnative-book
 [markdownlint]: https://github.com/DavidAnson/markdownlint
 [mdbook-admonish]: https://github.com/tommilligan/mdbook-admonish
@@ -70,3 +70,7 @@ Like godot-rust itself, the godot-rust book is licensed under [MPL 2.0][mpl].
 [mpl]: https://www.mozilla.org/en-US/MPL
 [oxipng]: https://github.com/shssoichiro/oxipng
 
+<br>
+
+[^gdnative-book]: For Godot 3, there is the older [gdnative-book].
+[^mdbook]: mdBook 0.5 contains breaking changes, and we can't support it until plugins catch up. Right now it offers no features that would benefit us.

src/register/properties.md

@@ -105,23 +105,31 @@ You can also declare both attributes on the same field. This is in fact necessar
 
 ## Enums
 
-You can export Rust enums as properties. An exported enum appears as a drop-down field in the editor, with all available options.
+You can export Rust enums as properties, as long as they are C style enums (no associated data per variant).
+An exported enum appears as a drop-down field in the editor, with all available options.
 In order to do that, you need to derive three traits:
 
-- `GodotConvert` to define how the type is converted from/to Godot.
-- `Var` to allow using it as a `#[var]` property, so it can be accessed from Godot.
-- `Export` to allow using it as a `#[export]` property, so it appears in the editor UI.
+- [`GodotConvert`][api-godotconvert] to define how the type is converted from/to Godot.
+- [`Var`][api-var] to allow using it as a `#[var]` property, so it can be accessed from Godot.
+- [`Export`][api-export] to allow using it as a `#[export]` property, so it appears in the editor UI.
+
+Additionally, it can make sense to derive following standard traits:
+
+- `Clone`: it is possible without, but then you need to implement `Var` manually. The reason is that `Var` also provides Rust getters when
+  used with `#[var(pub)]`, which require cloning the value.
+- `Default`: if there is a meaningful default value. If not, use `#[init(val = ...)]` on the field declarations to provide an initial value.
 
 Godot does not have dedicated enum types, so you can map them either as integers (e.g. `i64`) or strings (`GString`). This can be
 configured using the `via` key of the `#[godot]` attribute.
 
 Exporting an enum can be done as follows:
 
 ```rust
-#[derive(GodotConvert, Var, Export)]
+#[derive(GodotConvert, Var, Export, Default, Clone)]
 #[godot(via = GString)]
 pub enum Planet {
-    Earth, // first enumerator is default.
+    #[default] // Rust standard attribute, not godot-rust.
+    Earth,
     Mars,
     Venus,
 }
@@ -210,6 +218,9 @@ As a general rule, try to stay close to Godot's own types, e.g. `Array`, `Dictio
 ```
 
 
+[api-godotconvert]: https://godot-rust.github.io/docs/gdext/master/godot/meta/trait.GodotConvert.html
+[api-var]: https://godot-rust.github.io/docs/gdext/master/godot/register/property/trait.Var.html
+[api-export]: https://godot-rust.github.io/docs/gdext/master/godot/register/property/trait.Export.html
 [api-derive-export]: https://godot-rust.github.io/docs/gdext/master/godot/register/derive.Export.html
 [api-derive-var]: https://godot-rust.github.io/docs/gdext/master/godot/register/derive.Var.html
 [api-var-export]: https://godot-rust.github.io/docs/gdext/master/godot/register/derive.GodotClass.html#properties-and-exports