Drop urllib3 in favor of public gist

docs/advanced.md

@@ -809,24 +809,31 @@ HTTPX's `Client` also accepts a `transport` argument. This argument allows you
 to provide a custom Transport object that will be used to perform the actual
 sending of the requests.
 
+### Writing custom transports
+
 A transport instance must implement the Transport API defined by
 [`httpcore`](https://www.encode.io/httpcore/api/). You
 should either subclass `httpcore.AsyncHTTPTransport` to implement a transport to
 use with `AsyncClient`, or subclass `httpcore.SyncHTTPTransport` to implement a
 transport to use with `Client`.
 
-For example, HTTPX ships with a transport that uses the excellent
-[`urllib3` library](https://urllib3.readthedocs.io/en/latest/), which can be
+### Examples
+
+#### urllib3 transport
+
+This [public gist](https://gist.github.com/florimondmanca/d56764d78d748eb9f73165da388e546e) provides a transport that uses the excellent
+[`urllib3` library](https://urllib3.readthedocs.io/en/latest/), and can be
 used with the sync `Client`...
 
 ```python
 >>> import httpx
->>> client = httpx.Client(transport=httpx.URLLib3Transport())
+>>> from urllib3_transport import URLLib3Transport
+>>> client = httpx.Client(transport=URLLib3Transport())
 >>> client.get("https://example.org")
 <Response [200 OK]>
 ```
 
-Note that you'll need to install the `urllib3` package to use `URLLib3Transport`.
+#### Custom transport
 
 A complete example of a custom transport implementation would be:
 

docs/compatibility.md

@@ -81,3 +81,11 @@ Besides, `httpx.Request()` does not support the `auth`, `timeout`, `allow_redire
 ## Mocking
 
 If you need to mock HTTPX the same way that test utilities like `responses` and `requests-mock` does for `requests`, see [RESPX](https://github.com/lundberg/respx).
+
+## Networking layer
+
+`requests` defers most of its HTTP networking code to the excellent [`urllib3` library](https://urllib3.readthedocs.io/en/latest/).
+
+On the other hand, HTTPX uses [HTTPCore](https://github.com/encode/httpcore) as its core HTTP networking layer, which is a different project than `urllib3`.
+
+If you're transitioning from Requests to HTTPX, you might want to consider using HTTPX with an [`urllib3` custom transport](/advanced#urllib3-transport) at first, so that `urllib3` is retained as the underlying HTTP networking implementation, allowing you to deal with any differences in behavior as a second phase.

httpx/__init__.py

@@ -38,7 +38,6 @@
 from ._models import URL, Cookies, Headers, QueryParams, Request, Response
 from ._status_codes import StatusCode, codes
 from ._transports.asgi import ASGITransport
-from ._transports.urllib3 import URLLib3ProxyTransport, URLLib3Transport
 from ._transports.wsgi import WSGITransport
 
 __all__ = [
@@ -99,8 +98,6 @@
     "WriteError",
     "WriteTimeout",
     "URL",
-    "URLLib3Transport",
-    "URLLib3ProxyTransport",
     "Cookies",
     "Headers",
     "QueryParams",