Beraisa: For all Mesim (except for a parent) one tears a Tefach. For a parent one tears until he bares his heart.
R. Avahu: We learn from "Va'Yachazek David bi'Vgadav va'Yikra'em". 'Holding' always refers to at least a Tefach.
For all Mesim, even if one is wearing 10 garments it suffices to tear the outermost one. For a parent one tears all of them.
One need not tear the Apikarsus (this will be explained).
Both men and women tear;
R. Shimon ben Elazar says, a woman tears her inner garment, turns it around (so the tear will be in back), then tears the outer garment (so she will not be exposed).
For all Mesim, one may divide before the border, or not divide. For a parent one must divide;
R. Yehudah says, any tear in which one does not divide is meaningless.
R. Avahu: He learns from "Va'Yachazek bi'Vgadav va'Yikra'em li'Shnayim Kera'im". "Va'Yikra'em" already connotes two, so "li'Shnayim Kera'im" must teach that they should look like two.
For all Mesim, one may Sholel (sew back unevenly) after seven days and Me'acheh (sew back properly) after 30 days. For a parent, one may Sholel after 30 days, but he may never Me'acheh. A woman is Sholel immediately for her dignity.
For all Mesim, one may tear by hand or using a Keli. For a parent one must tear by hand.
For all Mesim, one tears mibi'Fnim (from the inside). For a parent one tears mib'Chutz (from the outside).
The Rif and Rosh (3:43) bring these teachings verbatim.
Rosh (ibid.): Rashi explains 'mibi'Fnim' to mean in a (different) room, away from people. The Ritz Gei'us says that he sticks his hand underneath The Ramban says that 'mibi'Fnim' (as opposed to 'bi'Fnim') supports the Ritz Gei'us.
Note: The Kesef Mishneh also cites Rashi to say this. In our texts and that of the Radvaz, Rashi explains like the Ritz Gei'us.
Nimukei Yosef (DH Mavdil): For a parent one must tear the border around the neck opening, in order that the torn parts will separate from each other. Sholel is plaited; Me'acheh is permanently sewn. A woman is Sholel immediately. It is not dignified for her garments to be torn.
Rambam (Hilchos Evel 8:2): The tear must be a Tefach. One need not separate the edge of the garment. One may tear with a Keli. He may tear inside not in front of people. Therefore, he may put his hand inside and tear covertly.
Kesef Mishneh: The Rambam holds that 'mibi'Fnim' includes both the Perushim of Rashi (in a different room) and the Ritz Gei'us (he sticks his hand underneath).
Rambam (ibid.): It suffices to tear the outermost garment.
Rambam (3): This refers to other relatives. For a parent one tears until he bares his heart. He does not tear with a Keli, rather, by hand. One tears from the outside, in front of everyone. He tears all the garments he is wearing. If he does not tear the undergarment that clings to his skin, it is not Me'akev.
Rosh (3:43): Rashi says that Apikarsus is a head turban that hangs down in front of him. Since it is not a garment, it is not Me'akev. The Ra'avad says that it does not say 'one need not tear it', rather, 'it is not Me'akev'. This shows that l'Chatchilah one should tear it for a parent. We infer that other Begadim are Me'akev. The Ramban says that l'Chatchilah, one need not tear it. There is an argument in a Beraisa. R. Binyamin says that one tears it. This implies that the first Tana, who says that it is not Me'akev, does not require tearing at all. The Aruch says that Apikarsus is an undergarment open at the shoulders. Since it is merely to absorb perspiration, it is not Me'akev.
Nimukei Yosef (DH v'Apikarsuso): Apikarsus is covering the tear so it is not visible.
Shulchan Aruch (YD 340:9): For all relatives it suffices to tear a Tefach on the outermost garment. For a parent he must tear all the garments he is wearing, until he bares his heart. If he did not he was not Yotzei, and we rebuke him as long as he is wearing the garments, even after 30 days.
Taz (6): We tear on the right for other relatives, and on the left for a parent, for then one must bare his heart.
Shulchan Aruch (10): One need not tear Apikarsus. Some say that this is an undergarment that clings to the skin to absorb perspiration. Other say that it is the Kafa (overcoat). The custom is not to tear the Kafa, even for a parent. We do tear the Kamiza (undershirt) for a parent.
Rema: Here, the custom is not to tear the linen undergarment for perspiration, nor the outer mantle. We tear everything else for a parent. For other relatives we tear the garment under the outer mantle.
Beis Yosef (DH v'Apikarsuso): Most say that one need not tear the Apikarsus. The Rambam and Rosh say that this is the innermost garment. Chachmei Tzarfas say that the outermost cloak is exempt, for it is worn merely for Tzeni'us. According to the Rambam this is torn for all Mesim. Maharam would tear it for a parent, but not for other Mesim. Hagahos Maimoniyos did not understand this. If it is exempt for other Mesim, it is exempt for parents! This is not difficult. Maharam was unsure. He did not tear it for other Mesim, for perhaps one is not Yotzei through this.
Taz (5): Mas'as Binyamin says that the Rema does not exempt the outer mantle, rather, a shawl around the neck that hangs down. He supports himself from the Agudah. It is unreasonable to say that the Rema refers to this. An Avel does not wear such a shawl! Also, the Agudah exempts only outer garments that are not normally worn in the house. The law does not depend on what is important, rather, on what is worn all the time. One should not be stringent to tear the outer mantle, lest one tear only it and he will not be Yotzei.
Shulchan Aruch (11): Men and women tear the same way, except that a woman tears her inner garment, turns it in back of her, then tears the outer garment.
Shach (22): This refers to tearing for a parent. Even though we do not tear the undergarment, it is indecent for her undergarment to be visible.
Mordechai (brought in Beis Yosef DH Echad): R. Shimon ben Elazar says that a woman tears differently, but Chachamim disagree. The Halachah follows Chachamim. Others say that we follow the lenient opinion in mourning. This is wrong. The Gemara says that this rule does not apply to Kri'ah. We are not concerned lest men have Hirhurim at such a time.
Beis Yosef (ibid.): Also the Rambam does not distinguish men from women. The Tur is lenient like R. Shimon ben Elazar. Perhaps he holds that the first Tana does not argue. Alternatively, R. Shimon's reasoning is better. We are concerned lest men who are not mourners have Hirhurim!
Shulchan Aruch (12): For all relatives one may leave the edge of the garment intact and tear below it, or he may tear the entire edge. For a parent he must tear the entire edge.
Shulchan Aruch (13): For all relatives one may tear inside not in front of people. Therefore, he may put his hand inside and tear covertly. For a parent he must tear outside in front of everyone.
Shulchan Aruch (14). For all Mesim, one may tear by hand or using a Keli. For a parent he must tear by hand.
Shulchan Aruch (15). For all Mesim, one may Sholel (sew unevenly) after seven days and be Me'acheh (sew evenly) after 30 days. For a parent one may be Sholel after 30 days; he may never be Me'acheh. A woman is Sholel immediately, for her dignity.