In figure 1, a Tibetan word or morpheme consists of not more than 7 letters, in which the base letter(Ba) is the core letter and the first one in structural sorting order, then the rest of the order is prefixed letters(Pr), head letters(Up), subjoined letters(Lw), vowels(V), suffixed letters(Sx).
except the base letters, any other letters may be absent in the structure.