**3. Elevate awareness of parentLocale to implementers.
People who filter CLDR data must recognize that if they filter out locale X, then they also have to filter out all of X's descendants. Or to put it another way, if they include locale X, they have to include all of X's ancestors.
For example, if they filter out pt_PT, then it invalidates all of its children [pt_CH, pt_CV, pt_GQ, pt_GW, pt_LU, pt_MO, pt_MZ, pt_ST, pt_TL|pt_AO,], and they need to filter each of them out also.
I doubt that this is clear implementers who might be filtering data. I strongly suspect not: the parentLocale data is treated like something simply internal to CLDR or ICU, and not surfaced clearly. We are probably only saved by the fact that many people don't filter them out, or if they do, they are unlike to keep the child but not the parent in these cases (pt_PT, zh_Hant_HK).
Ideas for how to do this?