Sometimes it takes talking to somebody new to Rails to recall the little blessings that I've come to take for granted (which I use to be doing by myself over and over and over again...) For example, these HTML inputs

<input name="person[0][name]" />
<input name="person[0][email]" />
<input name="person[1][name]" />
<input name="person[1][email]" />
<input name="person[2][name]" />
<input name="person[2][email]" />

when submitted, simply gives me regular, hierarchical hashes (not custom classes like PersonFormArray)

params["person"]["0"] # { "name" => ..., "email" => ... }
params["person"]["1"] # { "name" => ..., "email" => ... }
params["person"]["2"] # { "name" => ..., "email" => ... }

Some might disagree and say its simpler in some JEE framework where inputs and objects are paired for you automatically. What usually goes on, is that the binding is opaque and couples the implementation on two sides (view/controller or view/model). Stifling.

In Rails (ActionPack), the "binding" is only a transparent naming convention. Hence, there is no coupling and more flexibility. 

<input name="person[2][silly_requirement]" />

Will make the hash, without fuss, become

params["person"]["2"] 
# {"name" => ..., "email" => ..., "silly_requirement" => ...}