about action

   <extension
         point="org.eclipse.ui.actionSets">
         <action
               definitionId="org.eclipse.dltk.ui.edit.text.script.open.type.hierarchy"
               label="%OpenTypeHierarchyAction.label"
               retarget="true"
               menubarPath="navigate/open.ext"
               id="org.eclipse.dltk.ui.actions.OpenTypeHierarchy">
         </action>
      </actionSet>
   </extension>

    <extension
           point="org.eclipse.ui.views">

        <view
              name="%ScriptExplorerView.name"
              icon="$nl$/icons/full/eview16/package.gif"
              category="org.eclipse.dltk.ui.main"
              class="org.eclipse.dltk.internal.ui.scriptview.ScriptExplorerPart"
              id="org.eclipse.dltk.ui.ScriptExplorer">
        </view>

   </extension>
  
   <extension
         point="org.eclipse.ui.actionSetPartAssociations">
      <actionSetPartAssociation
            targetID="org.eclipse.dltk.ui.A_OpenActionSet">
         <part id="org.eclipse.dltk.ui.ScriptExplorer"/>
      </actionSetPartAssociation>
 </extension>

 

 

ScriptExplorerPart#createPartControl(then call fillActionBars()),NavigateActionGroup,OpenViewActionGroup#createSiteActions

 

        fOpenTypeHierarchy= new OpenTypeHierarchyAction(site);
        fOpenTypeHierarchy.setActionDefinitionId(IScriptEditorActionDefinitionIds.OPEN_TYPE_HIERARCHY);

 

 

IScriptEditorActionDefinitionIds.OPEN_TYPE_HIERARCHY equals to "org.eclipse.dltk.ui.edit.text.script.open.type.hierarchy"

 

 

 

if the retarget property of the action tag is true,view and editor parts may supply a handler for
 this action using the standard mechanism for setting a global action handler on their site using this
 action's identifier. If this attribute is true, the class attribute should not be supplied.

 

we can see the retargeted actionset is associated with class ScriptExplorerPart,so we can find the actual action OpenTypeHierarchyAction step by step.