I'm sure there are more classes and tags, but that hopefully should give you a solid place to start.
EDIT - You can also strip out or ignore anything inside of the ordered list for references - <ol class="references">...</ol>
Also, some pages aren't documented in the same way, so something like this page - https://en.wikipedia.org/wiki/X_Window_System - doesn't have any classes or easy way to parse it for the References section even though the Notes section was set up in a more organized way. However, you could take note that the <span> tag contains class="mw-headline" id="References" and the text value is also References and then ignore everything until the next <span> begins.