module RubyXL::WorkbookConvenienceMethods

def register_new_font(new_font, old_xf)
  new_xf = old_xf.dup
  new_xf.font_id = fonts.find_index { |x| x == new_font } # Reuse existing font, if it exists
  new_xf.font_id ||= fonts.size # If this font has never existed before, add it to collection.
  fonts[new_xf.font_id] = new_font
  new_xf.apply_font = true
  new_xf
end