Attributes @resp and @cert can be used here as elsewhere. A @source attribute is also available to indicate that another witness supports the reconstruction:
<p>ath ŝeir <supplied reason="omitted" source="AM02-152">mundu</supplied> sundr ganga</p>
When missing text cannot be confidently reconstructed, the <gap> element should be used. Its @reason attribute explains the reason for the omission and its @extent attribute indicates its presumed size.
<gap reason="damage" extent="7cm"/>