[Accepted at the November, 2020 meeting as part of paper P1787R6 and moved to DR at the February, 2021 meeting.]

Although 6.4.9 [basic.scope.temp] now describes the scope of a template parameter, the description of unqualified name lookup in 6.5.3 [basic.lookup.unqual] do not cover uses of template parameter names. The note in 6.5.3 [basic.lookup.unqual] paragraph 16 says,

the rules for name lookup in template definitions are described in 13.8 [temp.res].

but the rules there cover dependent and non-dependent names, not template parameters themselves.