def extra_context_request_processor(page, request):
    """
    Fills ``request._feincms_extra_context`` with a few useful variables.
    """
    request._feincms_extra_context.update(
        {
            # XXX This variable name isn't accurate anymore.
            "in_appcontent_subpage": False,
            "extra_path": "/",
        }
    )

    url = page.get_absolute_url()
    if request.path != url:
        request._feincms_extra_context.update(
            {
                "in_appcontent_subpage": True,
                "extra_path": re.sub(
                    "^" + re.escape(url.rstrip("/")), "", request.path
                ),
            }
        )

    Fills ``request._feincms_extra_context`` with a few useful variables.
    
feincms/module/page/processors.py