About ksus yoim/lailah, it got me thinking about our tallis katan.
How would you define ksus yoim or ksus lailah? i can think of two contrasting ways:
Simply, ksus yoim is any beged made to be worn by day, and ksus lailah is any beged made to be worn at night.
– this would mean, that is someone had the (strange) minhag to wear pajamas during the day, that would be considered ksus yoim for him (although it is possible that this would only be true if the beged was made specifically for him).
Or, and this is what i think is closer to the truth; ksus yoim means a day beged. A day beged is something that has a couple of purposes, such as to keep you warm, or to protect you from the sun, or to look presentable.
A night beged’s utility is for the night, mainly to keep one comfortable.
If someone wears pajamas during the day, it is still a night beged, and if someone wears a suit to bed, it is still a day beged, by definition.
So, according to the second definition here, where does our tallis katan fit in? Seemingly it is neither, it does not have the function of a night beged, nor does it have the function of a day beged. Since it needs to be a day beged to be chayav, it should be pattur from tzitzis!
Something to think about…