code: def add(font)
           if font.instance_of?(Font)
              @fonts.push(font) if @fonts.index(font).nil?
           end
           self
        end
docs: This method adds a font to a FontTable instance. This method returns
   a reference to the FontTable object updated.
  
   ==== Parameters
   font::  A reference to the font to be added. If this is not a Font
           object or already exists in the table it will be ignored.