אורח חיים שס״בOrach Chayim 362

Se’if 1א׳

כָּל מְחִצָּה שֶׁלֹּא נַעֲשֵׂית לָדוּר בְּתוֹכָהּ, אֶלָּא לִצְנִיעוּת אוֹ לִשְׁמֹר מַה שֶּׁיִּתְּנוּ בְּתוֹכָהּ אוֹ לִישֵׁב בָּהּ כְּדֵי לִשְׁמֹר הַשָּׂדוֹת, הִיא מְחִצָּה לְטַלְטֵל מַה שֶּׁבְּתוֹכָהּ, אֲבָל אֵינָהּ מְחִצָּה לַעֲשׂוֹת מַה שֶּׁבְּתוֹכָהּ מֻקָּף לְדִירָה אִם הוּא יוֹתֵר מִב' סְאָתַיִם. הִילְכָּךְ אִילָן שֶׁעֲנָפָיו יוֹרְדִים לְמַטָּה, אִם אֵינָם גְּבוֹהִים שְׁלֹשָׁה מִן הָאָרֶץ וְעִקָּרָן בַּמָּקוֹם שֶׁמְּחֻבָּרִין לָאִילָן הוּא גָּבוֹהַּ עֲשָׂרָה, חָשִׁיב מְחִצָּה וּמֻתָּר לְטַלְטֵל בְּכֻלּוֹ; וְהוּא שֶׁיְּמַלֵּא הָאֲוִיר שֶׁבֵּין הָעֲנָפִים בְּעֵצִים אוֹ בְּקַשׁ, וְיִקְשֹׁר הָעֲנָפִים שֶׁלֹּא יְנִידֵם הָרוּחַ, שֶׁכָּל מְחִצָּה שֶׁאֵינָהּ יְכוֹלָה לַעֲמֹד בְּרוּחַ מְצוּיָה, אֵינָהּ מְחִצָּה. וְדַוְקָא עַד בֵּית סְאָתַיִם, אֲבָל יוֹתֵר מִבֵּית סְאָתַיִם, לֹא, אֲפִלּוּ נְטָעוֹ לְכָךְ כֵּיוָן שֶׁאֵינוֹ עָשׂוּי לָדוּר בְּתוֹכוֹ אֶלָּא לְהִסְתּוֹפֵף בְּצִלּוֹ לִשְׁמֹר הַשָּׂדוֹת.

Which partition is called a partition for carrying. 12 sections: Any partition that was not made to dwell inside it, but rather for privacy, or to guard what is placed inside it, or to sit in it in order to guard fields — it is a valid partition for carrying within it, but it does not make what is inside it an enclosed dwelling (mukaf l'dirah) if it is more than two se'ah. Therefore, a tree whose branches hang down — if they are not three handbreadths above the ground, and their base where they connect to the tree is ten handbreadths high — it is considered a partition and one may carry throughout it, provided one fills the airspace between the branches with wood or straw and ties the branches so the wind does not move them, for any partition that cannot withstand an ordinary wind is not a valid partition. This applies only up to two se'ah, but more than two se'ah is not valid, even if the tree was planted for this purpose, since it is not made to dwell inside but to sit in its shade to guard the fields.

Se’if 2ב׳

תֵּל שֶׁגָּבוֹהַּ חֲמִשָּׁה וְהִשְׁלִימוֹ לַעֲשָׂרָה, שֶׁעָשָׂה עָלָיו מְחִצָּה גָּבוֹהַּ חֲמִשָּׁה, חֲשִׁיבָה מְחִצָּה לְטַלְטֵל וּלְכָל דָּבָר.

A mound that is five handbreadths high, and one completed it to ten by making a partition five handbreadths high on top of it — it is considered a valid partition for carrying and for all purposes.

Se’if 3ג׳

מְחִצָּה הָעוֹמֶדֶת מֵאֵלֶיהָ דְּהַיְנוּ שֶׁלֹּא נַעֲשֵׂית לְשֵׁם מְחִצָּה, כְּשֵׁרָה. מְחִצָּה שֶׁנַּעֲשֵׂית בְּשַׁבָּת, כְּשֵׁרָה וְהָנֵי מִלֵּי שֶׁנַּעֲשֵׂית בְּשַׁבָּת בְּשׁוֹגֵג, אֲבָל בְּמֵזִיד הַוְיָא מְחִצָּה לְהַחְמִיר לְחַיֵּב הַזּוֹרֵק מֵרְשׁוּת הָרַבִּים לְתוֹכָהּ אֲבָל לֹא לְהַתִּיר לְטַלְטֵל בְּתוֹכָהּ. וְהָנֵי מִלֵּי שֶׁלֹּא הָיָה שָׁם מְחִצָּה תְּחִלָּה, אֲבָל הָיְתָה שָׁם וֶהֱסִירָהּ וְחָזְרָה וְנַעֲשֵׂית, אֲפִלּוּ בְּמֵזִיד, חָזְרָה לְהֶתֵּרָהּ הָרִאשׁוֹן. כְּגוֹן שְׁנַיִם אוֹ שְׁלֹשָׁה שֶׁהִקִּיפוּ בְּמַחְצְלָאוֹת סְבִיבוֹתֵיהֶם בִּרְשׁוּת הָרַבִּים, וְהִבְדִּילוּ גַּם בֵּינֵיהֶם בְּמַחְצְלָאוֹת וְעֵרְבוּ יַחַד, מֻתָּרִים לְטַלְטֵל מִזֶּה לָזֶה. נִגְלְלוּ הַמַּחְצְלָאוֹת, נֶאֶסְרוּ. חָזְרוּ וְנִתְפָּרְסוּ, אֲפִלּוּ בְּמֵזִיד, חָזְרוּ לְהֶתֵּרָן הָרִאשׁוֹן.

A partition that stands on its own — meaning one not made for the purpose of being a partition — is valid. A partition made on Shabbat is valid, and this applies when it was made unintentionally (shogeg), but if done intentionally (meizid) it is a partition only to be stringent — to make one liable for throwing from a public domain into it — but not to permit carrying within it. This applies when there was no partition there previously; but if there was one, it was removed, and then re-formed, even intentionally, it reverts to its original permitted status. For example, two or three people who surrounded themselves with mats in a public domain and also divided between themselves with mats and made an eruv together — they are permitted to carry from one area to the other. If the mats were rolled up, it became forbidden; if they were spread out again, even intentionally, they revert to their original permitted status.