# Hexadecimal value 0x…, is an invalid character

Source: https://xmlvalid.com/errors/hexadecimal-value-is-an-invalid-character

> The document contains a control character that XML 1.0 does not allow.

The message, as .NET reports it: `'
', hexadecimal value 0x01, is an invalid character. Line 1, position 8.`

## Why it happens

- Control characters copied from a database or a binary field: 0x00 to 0x1F other than tab, line feed and carriage return.
- Writing such a character with `XmlWriter` fails the same way, with *is an invalid character*.

## How to fix it

- Remove the characters before writing the XML (`XmlConvert.IsXmlChar` tells which are allowed), or put binary data in Base64. `XmlReaderSettings.CheckCharacters = false` only hides the problem from your own reader.
- .NET throws an `XmlSchemaValidationException` at the first schema error unless `XmlReaderSettings.ValidationEventHandler` is set, which then receives every one with its line and position. A well-formedness error is an `XmlException` and ends reading whatever the settings.

## The same problem in xmlvalid

libxml2, which xmlvalid validates with, reports it as [PCDATA invalid Char value](https://xmlvalid.com/errors/pcdata-invalid-char-value): `PCDATA invalid Char value 1`

## Example that fails

```xml
<note>a
b</note>
```

## Fixed

```xml
<note>a b</note>
```