• References to non-instantiable classes
• References to classes that do not extend required class
• References to classes with inappropriate scope
• Tag and attribute values that do not match required pattern (for example, Java Identifiers)
• Tags that do not include required children tags or attributes
• Tags that define objects with duplicate names

Example:

<application>
    <module id="ExampleWebModule">
      <web> // Error: 'web-uri' child tag should be defined
        <context-root>ExampleWebApp</context-root>
      </web>
    </module>
</application>