In the tenth chapter of Maseches Shabbos, Mishnah 2, we take up the idea of carrying out in stages: the act of carrying out performed not all at once, but bit by bit and in stages.
"HaMotzi ochalin unesanan al ha'askufah":
A person carries food out of his house in a quantity large enough to make him liable, and places it on the askufah - the ledge at the entrance of the house.
The Gemara explains that the askufah under discussion here has the status of a karmelis: it is neither a private domain nor a public domain, but a kind of intermediate status situated between the two domains. From this it follows:
By Torah law: it is permitted to move an object from a private domain to a karmelis and from a karmelis to a private domain, and likewise from a karmelis to a public domain and from a public domain to a karmelis.
By rabbinic law: such moving is forbidden.
After he has placed the food on this askufah, the Mishnah rules: "bein shechazar vehotzi'an bein shehotzi'an acher - patur" - whether the one who carried it out took it himself from the askufah into the public domain, or whether another person did so.
Why is this? Even in the case where the one who carried it out is the one who completed the act, and the object began in a private domain and ultimately reached the public domain, there is no liability, because he did not perform the labor all at once. The carrying out was not accomplished in one continuous action, but was halted midway in the karmelis, and only afterward completed.
"Kupah shehi mele'ah peiros":
The second case in the Mishnah: a basket full of produce that was placed on "ha'askufah hachitzonah" - the outer askufah. This is not the askufah mentioned earlier, whose status is that of a karmelis, but an askufah whose status is that of a public domain: it is lower in height than the previous askufah, and it lies within three tefachim of the public domain, and therefore it is considered part of the public domain.
On the face of it we have here a complete act of carrying out from a private domain to a public domain, but the Mishnah qualifies this: "af al pi sherov haperos mibachutz - patur, ad sheyotzi es kol hakupah" - even though most of the produce is outside, he is exempt until he takes the entire basket out. The case is one in which part of the basket is still resting in the private domain and it is not entirely outside, and even though most of the produce inside it is already on the outer askufah, which has the status of a public domain, there is no liability.
The reason is this: as long as part of the basket is still in the private domain, the action is not considered an act of carrying out. The basket joins together all the produce inside it, and we view the pieces as attached to one another, as though we were dealing with a single object. Had we been dealing with one large piece of fruit, it would be obvious that as long as it has not entirely emerged there is no liability; and the Mishnah teaches the novel point that even in our case, where we are dealing with separate pieces and most of them are already outside in the public domain, the very fact that they are all inside a single basket, and that the basket itself is not yet entirely in the public domain, prevents the act of carrying out from being accomplished, and there is no liability at this stage.
In summary: the two clauses of the Mishnah teach the principle of carrying out in stages: a carrying out that was halted midway in a karmelis is exempt, since the labor was not performed all at once; and with a basket full of produce most of which is outside, he is exempt until he takes the entire basket out, since the basket joins the produce into a single object that has not yet fully emerged into the public domain.