From a reader…
Father, the subject Article IV says: “Celebrations of Mass as mentioned in art. 2 above may – observing all the norms of law – also be attended by faithful, who of their own free will, ask to be admitted.” What does the “observing all the norms of law” refer to?
That’s just standard boilerplate, legal language (servatis de iure servandis), to cover all the bases.
There are certain canons in the universal Code which regulate who can or cannot access certain chapels (e.g. can. 1226 establishes the concept of a private chapel which may limit attendance to a specific group, and can. 1223 on oratories, such as those in religious houses or seminaries, which also may have limited access). In addition, there may be cases wherein a priest is restricted to offering Mass only privately. There also may be situations in which a layperson has been penalized and thus restricted from entering a certain church, chapel, or oratory.