The (Italian) pair '*il luo libro' vs. 'il suo libro' (‘the his/her book’)
that is typical of Romance lends itself to an account of the first in terms of constraints also seen in the syntax of compounding, and to an account of the second that links its 's-', despite initial appearances, to what we think of as Romance reflexive 's-'. We might informally call this pair an instance of suppletion, as long as we recognize that calling it suppletion falls short of an account.