I wrote, > Changing the entry order to: > ᨽᩮᩣᨾᨶᩣᩮ > <LOW PHA, SIGN E, SIGN AA, MA, NA, SIGN AA, SIGN E> > ... forms the NAA ligature and the vowel re-ordering matches the > Lamphun graphic you sent. But that kludge probably breaks the > preferred encoding model/order.
On the other hand, do the script users normally input the NAA ligature sequence first and then add any additional signs or marks? If the users consider NAA to be a distinct "letter", then that might explain why a font developed by a user accomodates the ligation for the string "NA" + "AA" only when nothing else appears between them. If, for example, there's a popular input method or keyboard driver which puts "NAA" on its own key, then the users will be producing data which is "NA" plus "AA" plus anything else.
