The hreflang questions are some of the most interesting ones I see in the forums because it addresses things across domains, duplication, language handling, redirects and GoogleBot issues - it is a pretty important tag to use for sites that support multiple languages.
So when I spotted Google answer a question in the Google Webmaster Help forums on how to implement the proper Norwegian hreflang code for Norwegian language, I found it interesting.
Supposedly three language codes according to the ISO table, the language codes are; NO (Norwegian), NB (Norwegian Bokmål) and NN (Norwegian Nynorsk). The webmaster wants to know if he is safe just using NO and if so, would that cover NB and NN?
Google's Pierre Far said he should use NO:
Interesting question. I checked and you can use the 'NO' language code in this case.
The hreflang stuff can get really complicated, not because it is a hard topic but just because it can get confusing managing so many URLs and associations. Of course, you need to build a CMS that handles these well for you.
Forum discussion at Google Webmaster Help.