Return AttrError from attribute methods

Changelog.md

@@ -24,7 +24,9 @@
 - [#810]: Return `std::io::Error` from `Writer` methods.
 - [#811]: Split `NamespaceError` and `EncodingError` from `Error`.
 - [#811]: Renamed `Error::EscapeError` to `Error::Escape` to match other variants.
-- [#811]: `Bangtype` returns `SyntaxError` instead of `Error` since no other variant of `Error` is possible.
+- [#811]: Narrow down error return type from `Error` where only one variant is ever returned:
+  - `Bangtype` methods returns `SyntaxError`
+  - attribute related methods on `BytesStart` and `BytesDecl` returns `AttrError`
 
 [#227]: https://github.com/tafia/quick-xml/issues/227
 [#810]: https://github.com/tafia/quick-xml/pull/810

src/events/mod.rs

@@ -54,7 +54,7 @@ use crate::name::{LocalName, QName};
 #[cfg(feature = "serialize")]
 use crate::utils::CowRef;
 use crate::utils::{name_len, trim_xml_end, trim_xml_start, write_cow_string};
-use attributes::{Attribute, Attributes};
+use attributes::{AttrError, Attribute, Attributes};
 
 /// Opening tag data (`Event::Start`), with optional attributes: `<name attr="value">`.
 ///
@@ -297,7 +297,7 @@ impl<'a> BytesStart<'a> {
     pub fn try_get_attribute<N: AsRef<[u8]> + Sized>(
         &'a self,
         attr_name: N,
-    ) -> Result<Option<Attribute<'a>>, Error> {
+    ) -> Result<Option<Attribute<'a>>, AttrError> {
         for a in self.attributes().with_checks(false) {
             let a = a?;
             if a.key.as_ref() == attr_name.as_ref() {
@@ -1189,7 +1189,7 @@ impl<'a> BytesDecl<'a> {
     /// ```
     ///
     /// [grammar]: https://www.w3.org/TR/xml11/#NT-XMLDecl
-    pub fn encoding(&self) -> Option<Result<Cow<[u8]>, Error>> {
+    pub fn encoding(&self) -> Option<Result<Cow<[u8]>, AttrError>> {
         self.content
             .try_get_attribute("encoding")
             .map(|a| a.map(|a| a.value))
@@ -1231,7 +1231,7 @@ impl<'a> BytesDecl<'a> {
     /// ```
     ///
     /// [grammar]: https://www.w3.org/TR/xml11/#NT-XMLDecl
-    pub fn standalone(&self) -> Option<Result<Cow<[u8]>, Error>> {
+    pub fn standalone(&self) -> Option<Result<Cow<[u8]>, AttrError>> {
         self.content
             .try_get_attribute("standalone")
             .map(|a| a.map(|a| a.value))