This is really two questions, but it originally came up because our healer cleric is about to get access to Tearful Sonnet, which he is pretty grumpy about (but that's a different matter). In that spell, it says: "You cannot cast another spell through your spellcasting focus while concentrating on this spell." However, I can't find anything in the rules that says when you use a focus, you cast the spell through it. Heck, in A5e, I can't even find anything saying you need to handle it to cast a spell (unlike o5e which specifically states you need to be holding it), but I could just be missing something. Is there anything anywhere stating that you cast spells through a focus? What does this sentence refer to/mean?
To try to answer that, I looked at the Bard class's Art Specialty, but that leaves me with another question about this part: "Although spells can be cast without these instruments, only targets that are able to perceive your performance can benefit from this feature." I assume "this feature" means Art Specialty, but in what way do others "benefit" from it? For example, Percussion doubles your range, so if I'm not casting with drums, I already can't target creatures outside of my normal range, so whoever I am targeting is already not "benefiting" from the feature. I don't really understand what this is actually trying to say. Can someone help me out?
To try to answer that, I looked at the Bard class's Art Specialty, but that leaves me with another question about this part: "Although spells can be cast without these instruments, only targets that are able to perceive your performance can benefit from this feature." I assume "this feature" means Art Specialty, but in what way do others "benefit" from it? For example, Percussion doubles your range, so if I'm not casting with drums, I already can't target creatures outside of my normal range, so whoever I am targeting is already not "benefiting" from the feature. I don't really understand what this is actually trying to say. Can someone help me out?