Dandelions in Halacha

Yesterday morning I saw something that I had not seen for many moons. Unfortunately I didn't remember to write about it yesterday, so I guess today will have to suffice. What is it that I beheld? Dandelions. Gloriously yellow little weeds. Oh, the joy! No, really, I like them. No one gets angry when their little kid brings in a handful of dandelions. If they're presented with a handful of, let's say for argument's sake, Holland tulips, the reaction won't be so pleasant. Dandelions are free, and they're so cheery. In the summer when they die, they're not so pretty, but neither are the dog days for that matter.
Today is the first day of Rosh Chodesh Iyar, in honor of which I'll write a random Halacha of Rosh Chodesh, which can be found in Orach Chaim 419. For example, did you know that it is a Mitzvah to have extra food on Rosh Chodesh? And according to the Rif and the Rosh if Rosh Chodesh falls out on Shabbos then you should have extra food on Sunday in honor of Rosh Chodesh, because if you have it on Shabbos then everyone will think it's for Shabbos and they won't know it's meant to honor Rosh Chodesh. The Bach rules, however, that you should have the extra food on the day of Rosh Chodesh itself, even if it is Shabbos. The Magen Avraham says that we should make a compromise and extend the Seudah Shlishis, the third meal, past the ending of Shabbos, so that we can Bentch with Yaaleh V'yavo after Rosh Chodesh is (technically) over. By doing this we show that we're marking Rosh Chodesh specially. We also say Rtzei in this situation. According to the Shalah this Halacha only applies on Shabbos; if Rosh Chodesh falls out on a weekday and one extends their last meal into the next day then no mention of Rosh Chodesh is made in Bentching. The reason for this is that on Shabbos we have a Mitzvah to extend the holy day while on Rosh Chodesh there is no such obligation. The same would be true if the final day of Chanuka is on Shabbos, and he extends his meal, then (according to the Magen Avraham) he only says Rtzei and not Al Hanisim because the extension of Shabbos is obligatory while that of Chanuka is merely permissible. He would also hold that if Rosh Chodesh falls out on Motzei Shabbos, and the third meal is extended, then Yaaleh V'yavo, and not Rtzei, is said, because in truth the day is now Rosh Chodesh and not Shabbos.
According to the Beis Yosef (I think) we say that if Rosh Chodesh is on a Friday and a person extends his meal through the beginning of Shabbos we nevertheless say Yaaleh V'yavo and not Rtzei, even though it is Shabbos now, because we go after when the meal started. According to this, when Rosh Chodesh falls out on Motzei Shabbos and the meal is extended, we say Rtzei and not Yaaleh V'yavo, because the meal started on Shabbos. Tosafos says that if bread was eaten on Shabbos itself then both days must be mentioned, and the same would go for Bentching on Motzei Shabbos where bread was eaten after Shabbos was officially over. The Maharil says that if a person Davened Maariv on Motzei Shabbos then Rtzei is not said, because the guy Bentching would be in a bind-he ended Shabbos, but now he wants to start it up again!?
Therefore, says the Magen Avraham, if a person eats bread after Shabbos is officially over then he should only say Yaaleh V'yavo and not Rtzei. If he didn't eat bread after though, then he does say Rtzei and not Yaaleh V'yavo. According to the Maharam, if a person accepted Shabbos (by Davening) on Friday afternoon, while it's still day, he would only say Rtzei and not Yaaleh V'yavo, and so too on Motzei Shabbos. However, if he didn't Daven, even if the congregation did pray, he does mention Rosh Chodesh (on Friday night).
The Alter Rebbe writes that a person should therefore not extend their third Shabbos meal into Rosh Chodesh, because he is then faced with an impossible situation-either it's Shabbos, or Rosh Chodesh, but by definition it can't be both! Nevertheless, he says that if a person did this then he should Bentch with both Rtzei and Yaaleh V'yavo.
The Magen Avraham finishes off by quoting the Tur who says that all a person's food is decided on Rosh Hashanah, except what students bring to their schools on Rosh Chodesh. The Beis Yosef (again, I think it's him) that this means what the teacher is paid to teach his charges, while the Bach explains that the custom was for students to bring their teachers extra food on Rosh Chodesh, and this custom should not be abolished.

So, did you like that? I skipped a little in the middle, but I don't think it really changes anything I said above.