Switch to new serializer

Fixes tafia#252 - ok
Fixes tafia#280 - ok
Fixes tafia#287 - ok
Fixes tafia#343 - ok
Fixes tafia#346 - not ok
Fixes tafia#361 - ok
Partially addresses tafia#368
Fixes tafia#429 - ok
Fixes tafia#430 - ok

Changelog.md

@@ -14,6 +14,11 @@
 
 ### Bug Fixes
 
+- [#490]: Ensure, that serialization of map keys always produces valid XML names.
+  In particular, that means that maps with numeric and numeric-like keys (for
+  example, `"42"`) no longer can be serialized because [XML name] cannot start
+  from a digit
+
 ### Misc Changes
 
 - [#481]: Removed the uses of `const fn` added in version 0.24 in favor of a lower minimum
@@ -28,10 +33,12 @@
     (but text can represent a list as defined by `xs:list` type)
   - `#any` that is close to the previous `$value` behavior. Use it when you
     want to map field to any content of the field, text or markup
+- [#490]: Removed `$primitive=` prefix
 
 [#481]: https://github.com/tafia/quick-xml/pull/481
 [#489]: https://github.com/tafia/quick-xml/pull/489
 [#490]: https://github.com/tafia/quick-xml/pull/490
+[XML name]: https://www.w3.org/TR/xml11/#NT-Name
 
 ## 0.25.0 -- 2022-09-10
 

README.md

@@ -131,23 +131,6 @@ struct Foo {
 }
 ```
 
-### Serializing unit variants as primitives
-
-The `$primitive` prefix lets you serialize enum variants without associated values (internally referred to as _unit variants_) as primitive strings rather than self-closing tags. Consider the following definitions:
-
-```rust,ignore
-enum Foo {
-    #[serde(rename = "$primitive=Bar")]
-    Bar
-}
-
-struct Root {
-    foo: Foo
-}
-```
-
-Serializing `Root { foo: Foo::Bar }` will then yield `<Root foo="Bar"/>` instead of `<Root><Bar/></Root>`.
-
 ### Performance
 
 Note that despite not focusing on performance (there are several unnecessary copies), it remains about 10x faster than serde-xml-rs.

src/de/mod.rs

@@ -208,7 +208,6 @@ use std::num::NonZeroUsize;
 pub(crate) const TEXT_KEY: &str = "#text";
 /// Data represented by any XML markup inside
 pub(crate) const ANY_KEY: &str = "#any";
-pub(crate) const PRIMITIVE_PREFIX: &str = "$primitive=";
 
 /// Simplified event which contains only these variants that used by deserializer
 #[derive(Debug, PartialEq, Eq)]