1) HALACHAH: ONE WHO LEAVES TOWN FOR PURIM
OPINIONS: The Mishnah states that when a resident of an unwalled city finds himself in a walled city when Purim arrives, and when a resident of a walled city finds himself in an unwalled city, he reads the Megilah like his place of origin "if he plans to return to his place." If he does not plan to return to his place, he reads on the day on which his host city reads.
The Gemara explains that the Mishnah means that when a resident of a walled city plans to remain in the unwalled city throughout the night of the fourteenth of Adar, he reads the Megilah on the fourteenth with his host city even though he comes from a place which reads on the fifteenth. If he leaves before the end of the night (before daybreak), he reads on the same day as his hometown, on the fifteenth.
Does this explanation also apply to a resident of an unwalled city who is in a walled city on the night of the fourteenth? Does the person's status depend on where he finds himself on the night of the fourteenth or on the night of the fifteenth? If he comes from a walled city and spends the night of the fourteenth in an unwalled city, and on the night of the fifteenth he is back in his hometown, when does he read the Megilah?
(a) RASHI says that the Halachah in the two cases is determined by two different dates. Being in an unwalled city on the night of the fourteenth determines whether one must read on the fourteenth, while being in a walled city on the night of the fifteenth determines whether he must read on the fifteenth.
According to Rashi, it is possible that a person could be obligated to read the Megilah on both days -- such as when he was in an unwalled city throughout the night of the fourteenth, and during the day he went to a walled city and was there throughout the night of the fifteenth. In such a case, he would be obligated to read on both days. (The RAN, who agrees with Rashi's explanation, makes this point, and he cites support from the Yerushalmi.)
(b) The ROSH says that the Halachah in both cases is determined by where the person is on the night of the fourteenth. If the resident of a walled city is in an unwalled city on the night of the fourteenth, he not only becomes obligated to read on the fourteenth but he loses the obligation to read on the fifteenth even if he returns to his walled city before the night of the fifteenth. If the resident of an unwalled city is in a walled city on the night of the fourteenth, he loses the obligation to read on the fourteenth and becomes obligated to read the next day, on the fifteenth.
The RIF adds an important detail. The Halachah does not depend on whether the person actually stays in the city throughout the entire night of the fourteenth (or fifteenth according to Rashi). Rather, it depends on whether the person intended to stay in the city. If he intended to leave the host city before daybreak, he does not become obligated to read the Megilah with that city even if he ends up staying in the city. (The TAZ adds that this detail applies only l'Kula, as a leniency. That is, if one intended to leave the city before daybreak but ended up staying, he does not have to read the Megilah with that city. However, if one intended to stay in the city past daybreak but he ended up leaving during the night, his initial intention does not obligate him to read on the day that his host city reads. Rather, he reads with his hometown.)
What is the Halachah when one arrives in the host city after nightfall? The MISHNAH BERURAH (OC 688:12) writes that the day he reads is determined by where he intended -- at the time he embarked for the city -- to be at daybreak of the fourteenth (or fifteenth). He does not read the Megilah on the day of the host city if -- at the time he embarked for that city -- he intended to leave before daybreak of the fourteenth, but he does read with that city if he intended -- at the time he embarked -- to stay there past daybreak.
HALACHAH: The MISHNAH BERURAH cites the opinion of Rashi, that when a resident of an unwalled city travels to a walled city, the day on which he reads the Megilah depends on where he plans to be during the night of the fourteenth. When a resident of a walled city travels to an unwalled city, the day on which he reads depends on where he plans to be during the night of the fifteenth. The Mishnah Berurah (in Bi'ur Halachah) adds that one should not depend on this ruling with regard to reciting a Berachah, but he should ask a competent rabbinical authority how to conduct himself.
2) HOW TO SEW THE PARCHMENT OF A MEGILAH
OPINIONS: The Gemara teaches that when the verse refers to the Megilah as a "Sefer" (Esther 9:32), it teaches that the parchment may not be sewn with threads of flax (Pishtan) but only with threads of sinew (Gidin), like a Sefer Torah. When the verse also calls the Megilah an "Igeres" (Esther 9:26, 29), it teaches that one may be lenient and sew it with "three threads of Gidin."
What exactly is this leniency which is permitted for a Megilah but not for a Sefer Torah?
(a) Most Rishonim explain that the Gemara's leniency refers back to sewing the parchment with Pishtan (see RA'AVAN). Even though the Gemara said that the Megilah may not be sewn completely with Pishtan because of its status as a "Sefer," nevertheless if a few threads of Gidin are used the rest of the seam may be sewn up with Pishtan, even if there are only three threads of Gidin. The HAGAHOS MAIMONIYOS adds that one should preferably sew the rest with Pishtan rather than leave the rest without any thread, even though the Megilah would be invalid if only Pishtan was used. This Halachah is based on the principle of "Hashlamah," which teaches that when a gap needs to be filled, even an invalid object may be used to fill the gap (Sukah 17a). This is also the opinion of the RAMBAM (Hilchos Megilah 2:5, according to the Girsa in our editions).
(b) The ME'IRI says in the name of the RAMBAM that if the Megilah is sewn with three threads of Gidin, it is valid even if the rest of the width of the parchment is not sewn at all. When one sews the parchments of a Sefer Torah, he must sew the entire width with Gidin. In contrast, when one sews a Megilah, he may sew only three stitches and leave the rest unsewn. Accordingly, sewing the rest with threads of Pishtan may be more of a reason to invalidate the Megilah than leaving it partially unsewn.
The Me'iri's Girsa of the Rambam apparently is the Girsa which appears in the old manuscripts which read, "Eino Tzarich Litfor" (the rest does not need to be sewn up at all), and not, "Eino Tzarich Litfor b'Gidin" (which implies that it should be sewn with Pishtan).

19b----------------------------------------19b

2) THE AGE OF "CHINUCH" FOR A CHILD
QUESTION: The Gemara says that according to Rebbi Yehudah, a minor (Katan) who has reached the age of Chinuch may read the Megilah on behalf of adults. RASHI says that a child reaches the age of Chinuch at the age of nine or ten years old (nine for a more advanced child, ten for an average child). Similarly, Rashi in Erchin (2b) says that the age of Chinuch for the Mitzvah of blowing the Shofar on Rosh Hashanah is nine or ten years old.
However, the Gemara in Yoma (82a), which Rashi himself quotes as his source, gives the age of nine or ten specifically with regard to when a child must be trained to fast part of the day on Yom Kippur. Why does Rashi extend this age to include other Mitzvos such as Megilah and Shofar?
Moreover, the Gemara in Sukah (42a) gives various ages at which a child must begin to perform the Mitzvos of Lulav, Tzitzis, Tefilin, and Keri'as Shema. The age of Chinuch clearly depends on the requirements of that particular Mitzvah and the child's aptitude to fulfill those requirements. Hence, the same should apply to the Mitzvah of reading the Megilah; the age of Chinuch should be determined by when the child is able to understand the Megilah. Why does Rashi give a standard age which seems to be unrelated to the particular requirements of the Mitzvah of Megilah or Shofar? (TOSFOS to Erchin 2b, DH she'Higi'a)
ANSWERS:
(a) The MEI'RI in Chagigah (2a) writes that the primary age of Chinuch is nine or ten years old, as the Gemara says with regard to fasting on Yom Kippur. The other ages given for Chinuch apply only to Mitzvos which are very easy to do, and thus a child even younger than nine or ten is obligated, depending on his ability. The child is not obligated (by the requirement of Chinuch) to perform more difficult Mitzvos until he is nine or ten.
The Me'iri apparently understands that the Mitzvah of reading the Megilah is more difficult for a child than other Mitzvos because the entire Megilah must be read from a scroll (with no vowelization or cantillation marks). Similarly, the Mitzvah of Shofar is more difficult than other Mitzvos because it takes considerable skill and training to blow the Shofar properly. For that reason, Rashi writes that the age of Chinuch does not begin until nine or ten. (Even though the Mitzvah is to hear the Shofar and not specifically to blow it, and to hear the Megilah and not specifically to read it, it is logical to assume that when a child is unable to do the Mitzvah for himself when no one else is available, he has no obligation of Chinuch for the Mitzvah.)
(b) Perhaps there is a difference between a Mitzvah that involves an action and a Mitzvah that is done passively. When the Mitzvah involves an action, the age of Chinuch for that Mitzvah is when the child can perform that act. When the Mitzvah involves being passive and does not depend on doing an action, the age of Chinuch for that Mitzvah is when the child has the intellectual maturity to understand and appreciate the passive, Mitzvah experience.
For example, a child of any age is able (physically) to fast for one hour on Yom Kippur, but since the child does not appreciate the meaning of the experience he has no obligation to fast because of Chinuch. At the age of nine or ten, a child can understand why he is not eating. Similarly, the Mitzvos of listening to the Megilah and hearing the Shofar are passive acts which depend on a person's intellectual maturity to be able to appreciate the experience. For this reason, Rashi says that the Chinuch for these Mitzvos begins when the child is nine or ten years old, like the age of Chinuch for fasting on Yom Kippur. (See Insights to Erchin 2:3.)

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