This is the context you are looking for....
a = acquisition
b = bunched trade - average price
c = cash trade
d = distribution
e = automatic execution
f = intermarket sweep
g = bunched sold trade - opening/reopening trade detail
h = intraday trade detail
i = basket index on close transaction
j = rule 127 trade
k = rule 155 trade
l = sold last
n= next day
o = opened
p = prior reference price
r = seller
s = split trade
t = form t trade - pre/post market trade
u = extended hours trade - reported late or out of sequence
w = average price trade
y = yellow flagged regular trade
z = sold - out of sequence
