Update documentation for URI parsing types

See gh-33639

framework-docs/modules/ROOT/partials/web/web-uris.adoc

@@ -234,6 +234,34 @@ Kotlin::
 ======
 
 
+[[uri-parsing]]
+= URI Parsing
+[.small]#Spring MVC and Spring WebFlux#
+
+`UriComponentsBuilder` supports two URI parser types:
+
+1. RFC parser -- this parser type expects URI strings to conform to RFC 3986 syntax,
+and treats deviations from the syntax as illegal.
+
+2. WhatWG parser -- this parser is based on the
+https://github.com/web-platform-tests/wpt/tree/master/url[URL parsing algorithm] in the
+https://url.spec.whatwg.org[WhatWG URL Living standard]. It provides lenient handling of
+a wide range of cases of unexpected input. Browsers implement this in order to handle
+leniently user typed URL's. For more details, see the URL Living Standard and URL parsing
+https://github.com/web-platform-tests/wpt/tree/master/url[test cases].
+
+By default, `RestClient`, `WebClient`, and `RestTemplate` use the RFC parser type, and
+expect applications to provide with URL templates that conform to RFC syntax. To change
+that you can customize the `UriBuilderFactory` on any of the clients.
+
+Applications and frameworks may further rely on `UriComponentsBuilder` for their own needs
+to parse user provided URL's in order to inspect and possibly validated URI components
+such as the scheme, host, port, path, and query. Such components can decide to use the
+WhatWG parser type in order to handle URL's more leniently, and to align with the way
+browsers parse URI's, in case of a redirect to the input URL or if it is included in a
+response to a browser.
+
+
 [[uri-encoding]]
 = URI Encoding
 [.small]#Spring MVC and Spring WebFlux#