Reduplicative segments may have the same kinds of grammatical functions as affixes, and sometimes they are formally not easily distinguished from affixes. Therefore they must be glossed just like affixes, but at the same time they must be formally distinguished from affixes. This is achieved by providing the same kind of gloss for them as for grammatical formatives, but separating them by a tilde, as in and .

Rule 20. A reduplicative segment is glossed like an affix (i.e. by a configuration of grammatical category labels) and separated from its source by a tilde (~) both in T and in the gloss.

If reduplication occurs in the language with diverse functions, it may not seem appropriate to categorize it functionally like a grammatical affix. Instead, it may suffice to gloss it by RDP (reduplicative). The gloss of would then be ‘RDP~bad’.

If the tilde is not available as a boundary symbol, the ‘almost equal’ symbol ‘≈’ does the same service.

If the reduplicative element is not peripheral, boundary symbols may be put as follows:
In T, the reduplicative element is separated from its host by the tilde; the boundary symbol on its other side is the angled bracket enclosing it like an infix. The gloss of the reduplicative element is enclosed in the same way and precedes or follows the gloss of its host depending on the direction of reduplication, as in .