Board Thread:Questions and Answers/@comment-8072-20151230003114/@comment-16461120-20160105034834

I won't pretend to understand how they work, but if you look at the coding, Template:Twitter species the account and the Twitter button itself is simply coded in your example as:

Meanwhile, the part of the other template associated with that YouTube button seems to specify both the associated account and create the button as:

It's possible that Jamie might be able to explain it thoroughly or perhaps you can find more information here?