e fewer FontDicts in their
    FDArray than the default font, we have to match up the FontDicts in
    the different fonts . We do this with the FDSelect array, and by
    assuming that the same glyph will reference  matching FontDicts in
    each source font. We return a mapping from fdIndex in the default
    font to a dictionary which maps each master list index of each
    region font to the equivalent fdIndex in the region font.r