I encountered the word "chapeau" in the context of an U.N. treaty. It is defined in my dictionary as a three-cornered hat, but it seemed to be used in the sense of "aegis" or possibly "mission statement". Trawling its uses on the internet seems to suggest it may be a heading which defines the purpose of a chunk of legislative text, but I cant be sure of this....any ideas?

Hi Askewza, welcome.
I've only used it in French class but then I've never read a UN treaty. Anyone else less shallow than me?

Googling around on chapeau and treaty lead me to a definition of a chpaeau as the first paragraph in an article (of a formal document like a treaty). See this discussion.