3. Alternative commands

The above macro needs to be refined. If an emphasis element is implicitly or explicitly selected and this element has no role attribute or a role different from bold, we would like to add to it attribute role with value bold.

The following macro uses a choice element to do this:

<command name="convertToBold2">
  <macro repeatable="true" undoable="true"
         label="Convert to Bold">
        <command name="selectNode" 
                 parameter="self[implicitElement] emphasis" />
        <command name="convert" 
                 parameter="[implicitElement] emphasis" />
      <command name="putAttribute" parameter="role bold" />

The choice element will execute the first alternative which can be executed:

If all alternatives cannot be executed (this is tested before attempting to actually execute the choice construct), the whole choice construct cannot be executed.