[EXI] String Encoding in case of a string table miss

Hi 

       In case of a string table miss and value table miss we encode the
string or value as 

Length prefixed, length incremented by 1 string

Length prefixed, length incremented by 2 string

Can anybody explain the reason why the length of the string or value is
incremented by 1 or 2.

Regards

Santhanakrishnan