If you include knowledge articles in your management pack and fail to reference the maml schema, you’ll see this error during build time.

Error      80           Namespace prefix 'maml' is not defined

It’s a very easy fix. Simply add the highlighted below to the management pack fragment and build away.

<ManagementPackFragment SchemaVersion="2.0" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:maml="http://schemas.microsoft.com/maml/2004/10">