Perhaps the simplest tool that people use to distinguish between documentary wedding photography and other styles is that “documentary wedding photographers don’t take portraits”.
This definition is, in some ways however, somewhat misleading. Aside from the obvious caveat that many documentary wedding photographers are more than happy to do one or two posed portraits or groups if the couple would like them (they are merely not the central focus of a documentary photographer’s imagery) the truth is that, for us at least, as documentary style wedding photographers we’re actually looking for portraits all the time and through every part of a wedding day, we’re just not looking to stage them.