If some of you remember in GW1, when holding your cursor over your attributes (which more or less equals traits in GW2), a little box would appear describing the current attribute.
This tool tip would mostly contain switch sort of skills/weapons the line cater to.
fx. for the ranger:
The Marksmanship line would contain info about altering Signets and Longbow/harpoon skills.
Skirmishing alters Traps, Axe MH and all Bows.
Wilderness Survival alters Survival Skills, offhand skills, and sword/greatsword/spear skills.
Etc.
Ranger: My Main Man Ray