The command is not visible in my eclipse plugin - eclipse

Question

I am new to Eclipse plugin development. Recently, I downloaded a completed source code of an Eclipse plugin from another team. The popup menu of the plugin is not visible, so I just created a simple popup-menu-command for testing.
In the project, I only changed the plugin.xml to :
<?xml version="1.0" encoding="UTF-8"?>
<plugin>
<extension
point="org.eclipse.ui.commands">
<command
description="some description"
id="com.something.aCommand"
name="somet name">
</command>
</extension>
<extension point="org.eclipse.ui.menus">
<menuContribution locationURI="popup:org.eclipse.jdt.ui.PackageExplorer">
<command commandId="com.something.aCommand"
label="Create HTML" style="push">
</command>
</menuContribution>
</extension>
<extension
point="org.eclipse.ui.handlers">
<handler
class="com.something.aHandler"
commandId="com.something.aCommand">
</handler>
</extension>
</plugin>
(The aCommand and aHandler are nicknames of the real command and handler which do exist)
This sample is similar to the example here http://www.vogella.com/tutorials/EclipsePlugin/article.html#extending-the-eclipse-ide
And I tested it by Run as-> Eclipse Appliication, the right-click-pupup-command "Create HTML" is not visible.
Besides, this project does not contain fragment.e4mi file, does this mean it is a Eclipse 3 plug-in ? Because I find almost all eclipse plug-in tutorials are using fragment.e4mi and the e4 model fragment UI.
Environment:
Windows 10 64-bits
Eclipse Oxygen.1a Release (4.7.1a)

Answer 1

This is basically OK but is only contributing to the Package Explorer view (id org.eclipse.jdt.ui.PackageExplorer)
For Project Explorer to context menu id is org.eclipse.ui.navigator.ProjectExplorer#PopupMenu.
You can also use popup:org.eclipse.ui.popup.any to contribute to any menu.