Here is a piece of plugin.xml file of a standard Eclipse plugin
<!-- Extension points -->
<extension-point id="pluginContent" name="%expoint.pluginContent.name" schema="schema/pluginContent.exsd"/>
<extension-point id="newExtension" name="%expoint.newExtension.name" schema="schema/newExtension.exsd"/>
<extension-point id="templates" name="%expoint.templates.name" schema="schema/templates.exsd"/>
<extension-point id="samples" name="%expoint.samples.name" schema="schema/samples.exsd"/>
<extension-point id="targetProvisioners" name="%extension-point.name.0" schema="schema/targetProvisioners.exsd"/>
<extension-point id="launchShortcuts" name="%extension-point.name.1" schema="schema/launchShortcuts.exsd"/>
<!-- Extensions -->
<extension
point="org.eclipse.ui.perspectives">
<perspective
name="%perspective.name"
icon="$nl$/icons/eview16/plugins.gif"
class="org.eclipse.pde.internal.ui.PDEPerspective"
id="org.eclipse.pde.ui.PDEPerspective">
<description>
%perspective.description
</description>
</perspective>
</extension>
Please, what do these % and $ mean?