Following is the XML format:

```
<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE ncx PUBLIC "-//NISO//DTD ncx 2005-1//EN" "http://www.daisy.org/z3986/2005/ncx-2005-1.dtd">
<ncx xmlns="http://www.daisy.org/z3986/2005/ncx/" version="2005-1" xml:lang="en">
<head>
<meta name="dtb:uid" content="0000000000000"/>
<meta name="dtb:depth" content="1"/>
<meta name="dtb:totalPageCount" content="pageNumber"/>
<meta name="dtb:maxPageNumber" content="0"/>
</head>
</ncx>

```

I need to change the value of xml:lang but I don't know how to do it.

My C# Code:

```
xtabdoc.Root.Descendants().FirstOrDefault(el =>(string)el.Attribute(XNamespace.Xml + "lang") == "en");

```

It showed null.

Please help.