Defining PostHardcore and Metalcore

So when I was in high school the big post-hardcore bands were Silverstein, Funeral for a Friend, Thrice, and Finch. Those bands are not what I'd typically find here. With my favorites being We Came As Romans, The Word Alive, The Devil Wears Prada, etc. Bands that I personally always considered metalcore. I know the genres are supposedly getting really broad, but PH and MC are already a subgenre of a subgenre of a subgenre (Rock->Metal/Punk->Hardcore->Metalcore/PostHardcore). How far do we branch until its too much?

How would you define Post Hardcore and Metalcore?