great stuff! but i am confused with:
steem.getTrendingCategories(after, limit, callback);
steem.getBestCategories(after, limit, callback);
steem.getActiveCategories(after, limit, callback);
steem.getRecentCategories(after, limit, callback);

i have been trying to figure out what "after" stands for.
the documentation has rather little information on what those parameters stand for.

my first tought that it might be a date so i have tried several formats.
my second tought that it might be a tag, but didn't work either..

i also had a look into the official api documentation without any luck solving this.