Dear Hans and others, I'm usually use the \big, \Big, \bigg etc to get the size of parentheses, brackets and braces to be the size I want. I realize that the fences machinery is probably a cleaner way of doing this. I tried it a bit, and it usually gives the result I like. But sometimes not, and it seems that the way to change the size of the parentheses/brackets/braces is to use the factor key. 1) Are the different options none, auto NUMBER explained somehere? 2) Could one have, for exceptional cases where the default is not satisfactory, a keyword like factor=big for example, to get the same size as if one would have used \big? I am a bit confused. See the example below, with output (from latest standalone) attached. /Mikael PS: I would suggest to have italic = { feature = 'ss01', value = 1, comment = "Mathematical Alternative Lowercase Italic" }, set in lucida-opentype-math.lfg. In all books (on math) I have seen, I think this is what is used. %%% Example file: \setupbodyfont[lucidaot] \definemathfence[Set][left="007B,right="007D,command=yes] \startbuffer \startformula \Set{x\in\mathbb R~:~x^2=1} \stopformula \stopbuffer \startTEXpage[offset=3bp] \startformula \{x\in\mathbb R~:~ x^2=1\}%Too small \stopformula \startformula \bigl\{x\in\mathbb R~:~ x^2=1\bigr\}%I like this one \stopformula \startformula \Bigl\{x\in\mathbb R~:~ x^2=1\Bigr\}%Too big \stopformula \getbuffer \setupmathfence[Set][factor=1]%I like this one \getbuffer \setupmathfence[Set][factor=auto]%Too big \getbuffer %\setupmathfence[Set][factor=big]%Perhaps this could work? Or size=big or something %\getbuffer \stopTEXpage