oop - Extending classes or Interface or Abstract - PHP Child Classes for MVC ref: Vtiger -

i'm working in vtiger (mvc set up), modules contain mvc files. modules extend other modules extending class of other module. in case looking at, quote extends inventory module. outcome custom block inside quote, not whole new "page".

i want "block" whole module. should simple, except ran php "inheritance" issues. class need extend extended class already.

my logic was: ( b gets c ) works! gets b stuff. did not work.

the parent class class event extends calendar (shows event details / "final page")

the exiting "working" class class event extends inventory (creates new block)

i need these 2 classes communicate, since calendar "talks" events, , events talks inventory, variables unrelated, cannot output work, assume because of class "inheritance"

so direct question is: can existing child class extended?

• stack addresses in few posts i'm not able "grasp" how applies here since no variables shared, there should not bad obj calls.

here resources learning "connect" child classes:

• stack solution - should have worked
• php.net - example #2 extendable interfaces
• killerphp.com - when , why use interfaces

i tried explain reference problem may not php related rather understanding. thank in advance.