pub fn classify(&self) -> Category {
        match self.err.code {
            ErrorCode::Message(_) | ErrorCode::UnexpectedVisitType => Category::TypeUnmatched,
            ErrorCode::GetInEmptyObject
            | ErrorCode::GetInEmptyArray
            | ErrorCode::GetIndexOutOfArray
            | ErrorCode::GetUnknownKeyInObject => Category::NotFound,
            ErrorCode::Io(_) => Category::Io,
            ErrorCode::EofWhileParsing => Category::Eof,
            ErrorCode::ExpectedColon
            | ErrorCode::ExpectedObjectCommaOrEnd
            | ErrorCode::InvalidEscape
            | ErrorCode::InvalidJsonValue
            | ErrorCode::InvalidLiteral
            | ErrorCode::InvalidUTF8
            | ErrorCode::InvalidNumber
            | ErrorCode::NumberOutOfRange
            | ErrorCode::InvalidUnicodeCodePoint
            | ErrorCode::ControlCharacterWhileParsingString
            | ErrorCode::TrailingComma
            | ErrorCode::TrailingCharacters
            | ErrorCode::ExpectObjectKeyOrEnd
            | ErrorCode::ExpectedArrayCommaOrEnd
            | ErrorCode::ExpectedArrayStart
            | ErrorCode::ExpectedObjectStart
            | ErrorCode::InvalidSurrogateUnicodeCodePoint
            | ErrorCode::SerExpectKeyIsStrOrNum(_)
            | ErrorCode::FloatMustBeFinite
            | ErrorCode::ExpectedQuote
            | ErrorCode::ExpectedNumericKey
            | ErrorCode::RecursionLimitExceeded => Category::Syntax,
        }
    }
Categorizes the cause of this error.

- `Category::Io` - failure to read or write bytes on an I/O stream
- `Category::Syntax` - input that is not syntactically valid JSON
- `Category::Data` - input data that is semantically incorrect
- `Category::Eof` - unexpected end of the input data
src/error.rs