Adder and remover sidenote

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | all
| Fixed tickets | none

There are cases when you only want either adder or remover, important to know both of them need to be found if any is to work.
Yes, this is correct, see https://github.com/symfony/symfony/blob/2.5/src/Symfony/Component/PropertyAccess/PropertyAccessor.php#L589
If one of them is missing, none is used. 

I see 2.3 is throwing exceptions in such cases:
https://github.com/symfony/symfony/blob/2.3/src/Symfony/Component/PropertyAccess/PropertyAccessor.php#L409
but I guess this of behaviour has been considered unneeded as default  set* and collection->removeElement are used in case of adder / remover absence.

Also the part "If no ``addTag`` **and** ``removeTag`` method is found, the form will..." is semantically and logically correct. 
~(p^v) <=> ~p v ~v