Document Lazy Array manipulation in front

[jf-viguier]

It's a common case to try to add custom data to the lazy arrays in front for smarty (cart, product listing, product, ...)
How to use hooks actionPresent[entities], $presentedObject->offsetSet()
appendArray can also been used :
$productLazyArray->appendArray([
'extra_reference' => '123',
'extra_description' => 'Bla'
]);