There are places in the demo scripts that inherit things from Mx that are not necessary: like the fact that Mx couldn't read files with a labels line..
So in , we see:
data(twinData) twinVars <- c('fam','age','zyg','part','wt1','wt2','ht1','ht2','htwt1','htwt2','bmi1','bmi2')
Much easier to say
data(twinData) twinVars = names(twinData) # maybe with a comment so people know what is going on # 'fam','age','zyg','part','wt1','wt2','ht1','ht2','htwt1','htwt2','bmi1','bmi2'
Also enhances script re-use, avoids maintainance hassles and error.