Pure curiosity, I see that Mel Gibson is an adherent of Traditionalist Catholicism. Is this a part of "normal" Roman Catholicism, or some distinct branch? What are the differentiators here?
I found this information hidden at the bottom of your link:
After some more digging, I found that the main differences are:
It is worthy to note that the Vatican usually supports traditionalists, unless of course those traditionalists condemn modern day leadership or practices.
Most of this information was found on Wikipedia, I just tried to summarize it. There's plenty more information if you want to take a look!
EDIT (In response to a good comment by @Alypius): Here's a description of the different types of traditionalists, as described by an actual traditionalist. Religious preferences aside (I don't agree with the main gist of the article), the category description quoted below seems to be pretty succinct.
One must note that there is no single "Traditionalist Sect/Branch". The word "traditionalist catholic" may refer to anyone from someone who prefers Tridentine Mass over NOM to sedevacatists and followers of antipopes.
Some traditional catholics live in full communion with catholic church. They might be sceptical about SV II. They might disagree with some modernist tendencies.
The brotherhood of Saint Pius X is one of the biggest organisation of traditional catholics. It never rejected the pope, although during the pontificate of JP II it was excommunicated for consecrating bishops without pope's order. The unity was brought back by Pope Benedict XVI.
The "sedevacatist" is a term that generally describes someone that believes there is no pope. There is no single sedevacatist group and sedevacatists differ in the opinion which was the first unlawful pope.
Among the current antipopes there are also some that could be labeled as "traditionalists".