All these years and I’d never come across .invalid. From RFC 2606:

There is a need for top level domain (TLD) names that can be used for
creating names which, without fear of conflicts with current or
future actual TLD names in the global DNS, can be used for private
testing of existing DNS related code, examples in documentation, DNS
related experimentation, invalid DNS names, or other similar uses.

To safely satisfy these needs, four domain names are reserved as
listed and described below.


“.test” is recommended for use in testing of current or new DNS
related code.

“.example” is recommended for use in documentation or as examples.

“.invalid” is intended for use in online construction of domain
names that are sure to be invalid and which it is obvious at a
glance are invalid.

The “.localhost” TLD has traditionally been statically defined in
host DNS implementations as having an A record pointing to the
loop back IP address and is reserved for such use. Any other use
would conflict with widely deployed code which assumes this use.

On a related note, RFC 2606 is also where example.com, example.net, and example.edu are reserved.

HTTP Client Hints: DPR ( device pixel ratio )

From the world of “retina images are still kind of a pain”: clients could include DPR ( device pixel ratio ) details in image requests:

DPR hint automates device-pixel-ratio-based selection and enables delivery of optimal image variant without any changes in markup.

A request from the client for an image would look like:

GET /img.jpg HTTP/1.1
User-Agent: Awesome Browser
Accept: image/webp, image/jpg
DPR: 2.0

This would be wonderfully helpful to servers that can manipulate image results to best fit the capabilities of clients.

There is also discussion about a RW ( resource width ) header.