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Is there a main steemit blog? Hmm.. I have never come across it. They have also added various markdown commands from multi-markdown and started allowing more html. But nothing major.

Yes, it is @steemitblog, they usually post different announcements and such on it, check it out!

(I didn't really notice those markdown and html updates probably because I use the same ones all the time, but that's cool they did it.)