Check out example codes for "xml projects groups users". It will help you in understanding the concepts better.

Code Example 1

<group name="Readers" description="A group for users who have read access across the project">  
   <permissions>  
     <permission name="GENERIC_READ" class="PROJECT" allow="true" />  
     <permission name="GENERIC_READ" class="CSS_NODE" allow="true" />  
     <permission name="WORK_ITEM_READ" class="CSS_NODE" allow="true" />  
   </permissions>  
</group>

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