Also very important to point out; this same standardisation is missing on the TLD level.
Both for safeguarding internal use, and making a global TLD reserved on the global DNS zones. You'll find organisations using in production .local .dev (Taken by Google on 2014-11-20, followed by .app in 2015) *.zone (Taken by a LLC on 2014-01-09 ) as internal domains, with potential conflicts with the Internet's DNS resolution.
More importantly .dev [1] and .zone [2] are now valid TLDs, so watch out people!