'Get the kerning distance for font between *sym1* and *sym2*.
*fontX*: one of the TeX font names::
tt, it, rm, cal, sf, bf or default/regular (non-math)
*fontclassX*: TODO
*symX*: a symbol in raw TeX form. e.g., \'1\', \'x\' or \'\sigma\'
*fontsizeX*: the fontsize in points
*dpi*: the current dots-per-inch'

def get_kern(self, font1, fontclass1, sym1, fontsize1, font2, fontclass2, sym2, fontsize2, dpi):

    return 0.0
