KE, day is a function in the Financial Toolbox, and juliandate is a function in the Aerospace Toolbox. The fact that you're asking about both, and have R2015a, makes me wonder if perhaps you're missing those toolboxes, but are looking at documentation for the datetime data type, which has day and juliandate methods. It's new in R2014b.
>> d = datetime('now')
datetime is more or less a replacement for the combination of the suite of datenum/datevec/datestr functions, and in general, you want to use either datetime, or use the old functions, but not mix them.