Further clarifications in docs for what errors are returned. (#380)

Based on #281

src/nth.rs

@@ -7,7 +7,7 @@ use super::{BasicParseError, Parser, ParserInput, Token};
 /// Parse the *An+B* notation, as found in the `:nth-child()` selector.
 /// The input is typically the arguments of a function,
 /// in which case the caller needs to check if the arguments’ parser is exhausted.
-/// Return `Ok((A, B))`, or `Err(())` for a syntax error.
+/// Return `Ok((A, B))`, or an `Err(..)` for a syntax error.
 pub fn parse_nth<'i>(input: &mut Parser<'i, '_>) -> Result<(i32, i32), BasicParseError<'i>> {
     match *input.next()? {
         Token::Number {

src/parser.rs

@@ -698,7 +698,7 @@ impl<'i: 't, 't> Parser<'i, 't> {
     ///
     /// Successful results are accumulated in a vector.
     ///
-    /// This method returns `Err(())` the first time that a closure call does,
+    /// This method returns an`Err(..)` the first time that a closure call does,
     /// or if a closure call leaves some input before the next comma or the end
     /// of the input.
     #[inline]

src/rules_and_declarations.rs

@@ -34,7 +34,7 @@ pub trait DeclarationParser<'i> {
     ///
     /// Return the finished representation for the declaration
     /// as returned by `DeclarationListParser::next`,
-    /// or `Err(())` to ignore the entire declaration as invalid.
+    /// or an `Err(..)` to ignore the entire declaration as invalid.
     ///
     /// Declaration name matching should be case-insensitive in the ASCII range.
     /// This can be done with `std::ascii::Ascii::eq_ignore_ascii_case`,
@@ -78,7 +78,7 @@ pub trait AtRuleParser<'i> {
     /// Parse the prelude of an at-rule with the given `name`.
     ///
     /// Return the representation of the prelude and the type of at-rule,
-    /// or `Err(())` to ignore the entire at-rule as invalid.
+    /// or an `Err(..)` to ignore the entire at-rule as invalid.
     ///
     /// The prelude is the part after the at-keyword
     /// and before the `;` semicolon or `{ /* ... */ }` block.
@@ -122,7 +122,7 @@ pub trait AtRuleParser<'i> {
     ///
     /// Return the finished representation of the at-rule
     /// as returned by `RuleListParser::next` or `DeclarationListParser::next`,
-    /// or `Err(())` to ignore the entire at-rule as invalid.
+    /// or an `Err(..)` to ignore the entire at-rule as invalid.
     ///
     /// This is only called when `parse_prelude` returned `WithBlock`, and a block
     /// was indeed found following the prelude.
@@ -161,7 +161,7 @@ pub trait QualifiedRuleParser<'i> {
     /// Parse the prelude of a qualified rule. For style rules, this is as Selector list.
     ///
     /// Return the representation of the prelude,
-    /// or `Err(())` to ignore the entire at-rule as invalid.
+    /// or an `Err(..)` to ignore the entire at-rule as invalid.
     ///
     /// The prelude is the part before the `{ /* ... */ }` block.
     ///
@@ -180,7 +180,7 @@ pub trait QualifiedRuleParser<'i> {
     ///
     /// Return the finished representation of the qualified rule
     /// as returned by `RuleListParser::next`,
-    /// or `Err(())` to ignore the entire at-rule as invalid.
+    /// or an `Err(..)` to ignore the entire at-rule as invalid.
     fn parse_block<'t>(
         &mut self,
         prelude: Self::Prelude,
@@ -353,7 +353,7 @@ where
     }
 }
 
-/// `RuleListParser` is an iterator that yields `Ok(_)` for a rule or `Err(())` for an invalid one.
+/// `RuleListParser` is an iterator that yields `Ok(_)` for a rule or an `Err(..)` for an invalid one.
 impl<'i, 't, 'a, R, P, E: 'i> Iterator for StyleSheetParser<'i, 't, 'a, P>
 where
     P: QualifiedRuleParser<'i, QualifiedRule = R, Error = E>