Mishnah Berurah — משנה ברורה

When he was in a karmelit - That is a place where the prohibition to carry [things] is only on a rabbinic level. And therefore, it is not necessary [for him] to remove [his טלית] because human dignity overrides a rabbinic level prohibition. And even though ציצית is a Torah level mitzvah, and a Torah level mitzvah does not get overridden because of human dignity, nevertheless, it is still permitted, because the Torah did not say "Don't wear a garment without ציצית" (ie. in a negative term), rather it's a positive commandment to affix ציצית on it (the garment). And since [here] he can't affix [a valid] ציצית on Shabbos, he's not transgressing a positive commandment, and he's only [violating] a rabbinic level prohibition. And therefore, he is permitted [to carry it in a karmelit] because of human dignity and he is not required to remove the טלית. But [to carry] in a public domain, which is a Torah level [prohibition], he is required to remove it, whether it's a large טלית (that we use for prayers) or a small טלית (that we wear under our clothing throughout the day), and even if he will be left naked (ie. shirtless) by doing that, because human dignity does not override a Torah level prohibition like this in any situation. And below in the [section dealing with the] Laws of Shabbos, G-d willing, we will explain that there is a dispute if nowadays we have a public domain or not. And it appears, that if the tassel (ie. the winded up and knotted part of the ציצית) was intact, and the invalidation was only on the loose strings [that are hanging down past the last knot], we can join with the opinion of the R"i above who permits it (ie. the R"i holds that you measure the minimum length of string needed, if they were severed, from the tassel part. So if the tassel part was intact, then the ציצית are still valid), and one would not be required to remove it immediately, rather he should hurry to go to his home [and remove it there]....