Minor refactor.

src/custom_syntax.rs

@@ -335,7 +335,6 @@ impl Engine {
     /// * `Ok(None)`: parsing complete and there are no more symbols to match.
     /// * `Ok(Some(symbol))`: the next symbol to match, which can also be `$expr$`, `$ident$` or `$block$`.
     /// * `Err(ParseError)`: error that is reflected back to the [`Engine`], normally `ParseError(ParseErrorType::BadInput(LexError::ImproperSymbol(message)), Position::NONE)` to indicate a syntax error, but it can be any [`ParseError`].
-    ///
     pub fn register_custom_syntax_raw(
         &mut self,
         key: impl Into<Identifier>,