is there a way to send a message from an abstraction to the parent patch? I'd need this to let the abstractino create a subpatch in the parent patch

Can you just add an outlet to the abstraction and send the message through that?

I'd prefer not.
anyhow, what is the syntax to do that?

Add a [outlet] in the abstraction and it'll show up in the parent patch. Maybe I'm not understanding your question fully.

Otherwise you could use a global send/receive to communicate between the parent and abstraction patch:

i.e. in the abstraction add , and in the parent patch [r abstractionToParent]

Finally if you want multiple abstractions and want to address each one individually, add a unique variable as an argument to the abstraction:

i.e [abstractionName 1], then in the abstraction create a send called , and in the parent patch it'll send to
[r abstractionToParent-1]

The syntax for creating a subpatch should be something like [$1 canvas 0 0 0 0 0;(
The [ and ( symbols indicate that this is a message box, you should not include them in the command. The zeros are coordinates of the subpatch, not really sure what all five of them do, you'll have to experiment a bit. Finally the $1 is the name of the parent patch. Not really sure how to include a name for the subpatch in the command...hope this helps.

I'd use something like
|obj 0 0 pd my_subpatch(
|

to create the subpatch.

What I want to do is the abstraction to create a subpatch in the parent patch, but without passing any argument to the abstraction, and without even the need for the parent patch to have a name.
is this possible?

Anything is possible

http://www.pdpatchrepo.info/hurleur/dynamicSubpatch.zip

Thanks, I had already got to this point. But as you can see, you actually use the name of the parent patch - which is called pd-parent.pd - , and thus if you call [abstraction] from a patch that is not called parent.pd , this wouldn't work . Furthermore, shoud you have more than one patch called parent.pd , this would create subpatch in each of them, which I don't want.
I'm looking for something that just identifies the parent patch, whatever it may be

If you're on Pd-extended 0.43, you can use [iemguts/sendcanvas].