images/syllable.png (at https://w3c.github.io/tlreq/#syllable_structure in the text) says that ya, ra, la, sa are the subscribed letters. sa is listed there by mistake. cf e.g. images/subscripts.png.
Probably, it's wa that was meant here instead - though I'm not prepared to argue whether wa zur should be considered a proper subjoined letter or, with 'a chung, constitutes a separate class, neither am I properly familiar with the Tibetan tradition of formally analyzing its status.
images/syllable.png
(at https://w3c.github.io/tlreq/#syllable_structure in the text) says that ya, ra, la, sa are the subscribed letters. sa is listed there by mistake. cf e.g.images/subscripts.png
.Probably, it's wa that was meant here instead - though I'm not prepared to argue whether wa zur should be considered a proper subjoined letter or, with 'a chung, constitutes a separate class, neither am I properly familiar with the Tibetan tradition of formally analyzing its status.