Possibility to put tags: case, field, constant and operation in the left-operand and right-operand tags

Problem to solve

You can't put the tags field, constant, operation and in in the left-operand and right-operand tags without counting those in the operations tag.

Further details

For instance, the possibility of putting the following:

<right-operand>
  <case>
     <when left-field="MdsIde" left-table="mds" condition="is not null" >
       <then id="MdsIde" table="mds"/>
     </when>
  </case>
</right-operand>

Instead of:

<right-operand>
     <when left-field="MdsIde" left-table="mds" condition="is not null" >
       <then id="MdsIde" table="mds"/>
     </when>
</right-operand>

/label feature