#1
I was looking around on musiciansfriend.com and I saw that there are like a crap load of different models of the Martin D-28 and D-35 and various others. So what I want to know is whats the difference between say:

D-28
HD-28
D-28V
HD-28V

And also what is the difference between all of the Martin Models, i.e. Martin D-35 vs a D-28 vs a D-18 vs a D-41, D-45, etc.
#2
maybe the HD one are high-definition....

but i believe HD-28 has scalloped braces, which gives it more mature tone and also they have some other cosmetic diffrences like herringbone trim, tortoise pickguard.