Herbicide lables now have the chemical group number on them which helps one know the mode of action. This can be handy to make sure that the herbicides selected complement each other and also that it is appropriate for a given weed. There is a short paper that explains it well. I think after I get used to it I'll look for and use the info.
http://www.extension.iastate.edu/CropNews/2010/1220hartzler.htm
