Hi Anthony:

In message <668020702.20170911154217@inbox.ru>,
Anthony writes:
>I found that I can't set value of "__redirect_to" to the relative url.

That's correct and intentional. The __redirect_to (and _came_from)
parameter is accessible to the user or to any nasty malware in the
browser.

>Recently introduced examine_url() function will raise an error in such
>case because it expect only an absolute url.

From the comment right above that block:

       To try to prevent XSS attacks, validate that the url that is
       passed in is under self.base for the tracker. This is used to
       clean up "__came_from" and "__redirect_to" form variables used
       by the LoginAction and NewItemAction actions.

I assume the URL is generated by accessing the base url in the tracker
config and using that to generate an absolute url. For example:

    tal:attributes="value string:${request/base}${request/env/PATH_INFO}?${request/env/QUERY_STRING}"

What is your use case where this must be a relative url?