Hi, i want to use MSBuild to insert a custom xml element into web.config. After looking up online, i found such solution:

1) Store element in the .build file in projectextensions

<ProjectExtensions>
 <CustomElement name="CustomElementName">
  ...
 </CustomElement>
</ProjectExtensions>

2) Retrieve the element with GetValue

<Target name="ModifyConfig">
<XmlFile.GetValue Path="$(MSBuildProjectFullPath)"
               XPath="Project/ProjectExtensions/CustomElement[@name='CustomElementName']">
            <Output TaskParameter="Value" PropertyName="CustomElementProperty"/>
</XmlFile.GetValue>
</Target>

This will not work as i need to reference a namespace the .build project is using for it to find the needed element (checked the .build file with XPath Visualizer). So, i look up for a further solution and come to this:

<ItemGroup>
        <XmlNamespace Include="MSBuild">
            <Prefix>msb</Prefix>
            <Uri>http://schemas.microsoft.com/developer/msbuild/2003</Uri>
        </XmlNamespace>
</ItemGroup>

<Target name="ModifyConfig">
<XmlFile.GetValue Path="$(MSBuildProjectFullPath)" Namespaces="$(XmlNamespace)"
               XPath="/msb:Project/msb:ProjectExtensions/msb:CustomElement[@name='CustomElementName']"
                 >
            <Output TaskParameter="Value" PropertyName="CustomElementProperty"/>
</XmlFile.GetValue>
</Target>

But for some reason namespace is not recognized - MSBuild reports the following error:

C:...\mybuild.build(53,9): error : A task error has occured. C:...\mybuild.build(53,9): error : Message = Namespace prefix 'msb' is not defined.

I tried some variations of referencing it differently but none work, and there is not much about propertly referencing those namespaces online also. Can you tell me what am i doing wrong and how to do it propertly?