Calendar validation

Hello. I am wondering where the rendering of the calendar is defined? I see the function but I can’t find where it’s setup. I tried searching for information here on the WP calendar that is part of the style when you first setup WordPress but all I found was info about plug-ins. I couldn’t be sure if this was the same calendar.
At any rate, the reason I ask is that it doesn’t validate because of some ul and li tags. I’d like to fix it but can’t find the code for it.
Any help pointing in the right direction for finding the calendar is greatly appreciated. I’m just learning html and I’d rather learn it with some standards now rather than having to go back and clean it up later.
in advance, thank you and thank you already for the help this forum has been.