(SQL mode="mask")
    <query>
  
       SELECT username,email FROM users;

    </query>
    <mask>

      [link action="showuser" 
          username="<d>username</d>"
          ]<d>username</d>[/link],

      [link to="mailto:<d>email</d>"]<d>email</d>[/link] 
      <br>
  
    </mask>
  (/SQL)
  
Becomes :

 <SQL aXML_class="primary" mode="mask">
    <query>
  
       SELECT username,email FROM users;

    </query>
    <mask>

      <link aXML_class="tertiary"
            action="showuser" 
          username="<d>username</d>"
          ><d>username</d></link>,

      <link aXML_class="tertiary" 
                     to="mailto:<d>email</d>"
          ><d>email</d></link> 
      <br>
  
    </mask>
  </SQL>
  
Also when tags have tags embedded in their attributes like this :

<a b="<c>d</c>">data</a>

converting the expression to XML like this;

<a aXML_class="standard">
  <attr>b="<c aXML_class="standard">d</c>"</attr>
  <contents>data</contents>
</a>