This tag gives the id of the current page

The page ID is taken from the cfgpages. if for exemple the cfgpages contain the nodes

  <page name='/'>
    <page name='real-estate'>  
      <page name='residential'>  
        <page name='holiday-rentals' />
      </page>
    </page>
  </page>

if the current page name is the node holiday-rentals then result of <#page_id> will be /real-estate/residential/holiday-rentals/

<#page_id>