  In this comment, we reassess the underlying physics of the number sum rule
for dihadron fragmentation functions. We will argue that, currently, there are
no settled constraints on what constitutes a valid number density
interpretation for multihadron fragmentation functions. Imposing overly
restrictive criteria might lead to misinterpretating the data. Most
importantly, and on the basis of phenomenological analyses, the slightly
varying definitions used in previous work are not excluded from possessing
legitimate number density interpretations (up to the usual issues with
ultraviolet divergences and renormalization), so long as they are paired with
appropriate factorization theorems. We advocate for further theoretical
analyses to be challenged with experimental data, available at JLab or at the
future EIC.
