Hi, I am looking at the documentation of poly_collection. I will not be able to thoroughly review and test the library. But judging from the documentation, the problem is worth solving, and the approach to solve it is sound. I have one question/observation though. I am trying to figure out how preventing an incorrect insert() works. In the docs ( http://rawgit.com/joaquintides/poly_collection/website/doc/html/poly_collect...) it says that it will sometimes throw if it cannot determine the most derived type. In the class reference, I get: ( http://rawgit.com/joaquintides/poly_collection/website/doc/html/poly_collect... ) ``` (1) c.insert(x) (2) c.insert(it,x) Effects: If the type of the subobject of t is not registered, then if this type is T and T is acceptable, does the registration, otherwise throws. If t is not a non-const rvalue expression and the type of its subobject is not CopyConstructible, throws. Inserts an element with a subobject move constructed or copy constructed from the subobject of t: (1) at the end of the corresponding segment; (2) just before the position indicated by it, if it points to the corresponding segment, or at the end of the segment otherwise. Returns: An iterator to the newly inserted element. Complexity: Amortized constant time plus linear in the distance from the insertion position to the end of the segment. ``` And maybe it is just me, but I cannot make the sense of it. First, it refers to 't' but in the signatures we have an 'x'. Next, the first sentence has two "if"s and one "otherwise" and I do not know which "if" the "otherwise" binds to. I read it as saying: if T is derived from the interface (like class `warrior`) but is not movable (which implies that T is not "acceptable"), then the program will compile fine but will later throw an exception. Is my interpretation correct? But if so, why not refuse to compile instead? Maybe it would be better tom make the prose longer in "Effects" clause, but to make it harder for misinterpretation. Regards, &rzej;