13. The method of claim 6 , wherein: the glyphs of the master font are partitioned into a plurality of master font ranges ranked in an order of precedence established by a master font range ordering; and the one or more existing glyphs already in the extensible data structure are partitioned into one or more existing client font ranges consecutively enumerated to preserve the order of precedence established by the master font range ordering, wherein each of the one or more existing client font ranges corresponds to one of the plurality of master font ranges that contains each glyph in the existing client font range.
13. The method of claim 6 , wherein: the glyphs of the master font are partitioned into a plurality of master font ranges ranked in an order of precedence established by a master font range ordering; and the one or more existing glyphs already in the extensible data structure are partitioned into one or more existing client font ranges consecutively enumerated to preserve the order of precedence established by the master font range ordering, wherein each of the one or more existing client font ranges corresponds to one of the plurality of master font ranges that contains each glyph in the existing client font range. 15. The method of claim 13 , wherein the generated instructions include instructions for: establishing one or more new client font ranges, wherein each of the one or more new client font ranges corresponds to one of the plurality of master font ranges containing a glyph of the font subset that is not contained in any of the one or more master font ranges corresponding to the one or more existing client font ranges; consecutively enumerating a combined set of client font ranges comprising the one or more new client font ranges and the one or more existing client font ranges, wherein said consecutively enumerating the combined set of client font ranges preserves the order of precedence established by the master font range ordering; and placing each of the glyphs in the extensible data structure in the client font range whose corresponding master font range contains the glyph.