PHP_SELF vs PATH_INFO vs SCRIPT_NAME vs REQUEST_URI

Some practical examples of the differences between these variables:
Example 1. PHP_SELF is different from SCRIPT_NAME only when requested url is in form:
http://example.com/test.php/foo/bar

[PHP_SELF] => /test.php/foo/bar
[SCRIPT_NAME] => /test.php

(this seems to be the only case when PATH_INFO contains sensible information [PATH_INFO] => /foo/bar) Note: this used to be different in some older PHP versions (<= 5.0 ?).

Example 2. REQUEST_URI is different from SCRIPT_NAME when a non-empty query string is entered:
http://example.com/test.php?foo=bar

[SCRIPT_NAME] => /test.php
[REQUEST_URI] => /test.php?foo=bar

Example 3. REQUEST_URI is different from SCRIPT_NAME when server-side redirecton is in effect (for example mod_rewrite on apache):

http://example.com/test.php

[REQUEST_URI] => /test.php
[SCRIPT_NAME] => /test2.php

Example 4. REQUEST_URI is different from SCRIPT_NAME when handling HTTP errors with scripts.
Using apache directive ErrorDocument 404 /404error.php
http://example.com/test.php

[REQUEST_URI] => /test.php
[SCRIPT_NAME] => /404error.php

On IIS server using custom error pages
http://example.com/test.php

[SCRIPT_NAME] => /404error.php
[REQUEST_URI] => /404error.php?404;http://example.com/test.php

The PHP documentation can tell you the difference:

'PHP_SELF'

The filename of the currently executing script, relative to the document root. For instance, $_SERVER['PHP_SELF'] in a script at the address http://example.com/test.php/foo.bar would be /test.php/foo.bar. The __FILE__ constant contains the full path and filename of the current (i.e. included) file. If PHP is running as a command-line processor this variable contains the script name since PHP 4.3.0. Previously it was not available.

'SCRIPT_NAME'

Contains the current script's path. This is useful for pages which need to point to themselves. The __FILE__ constant contains the full path and filename of the current (i.e. included) file.

'REQUEST_URI'

The URI which was given in order to access this page; for instance, '/index.html'.

PATH_INFO doesn't seem to be documented...