I’m a web developer and set up many websites on my local server. As such, using localhost for all these sites just won’t cut it. I do what many typical developers do and have set up each on local domains, i.e.
And I reconfigure my local hosts file accordingly. However, when trying to embed a Twitter widget, these (perfectly valid according to the domain format spec) domains are rejected as invalid, making the Twitter widgets next to useless as I’m not going to deploy a widget to a live site without testing locally, and I shouldn’t have to change my local domain setup just because Twitter thinks it’s OK to ignore official specifications and just do its own thing.