Drupal 7 Core Module Function for node_save? In Drupal 7, i want to put a additional code when the Save button is Clicked (Saving) in "a content" form (New or Edit).

I don't want to know the hook (because i don't want to make an obvious Custom Module). Because i don't want to let other users know the operation by having a obvious Custom Module which will be listing inside the Module Panel. So i want to make a Silent Customization inside the Existing Drupal Core Module (correspondence Function). 

Thats why I just want to know the Function in the Core Modules which finally process the Node Save task.


Can anyone please describe which Function (in Core Modules) is finally processing the Drupal Node Save? (Save` finally may be for both New Item Insert or existing Item Edit.)
DO NOT HACK CORE

Now that's out of the way, let's continue.

The way I see it, you have a couple of options:

1) Use Rules.


  The rules module allows site administrators to define conditionally
  executed actions based on occurring events (known as reactive or ECA
  rules). It's a replacement with more features for the trigger module
  in core and the successor of the Drupal 5 workflow-ng module.


Although this will allow people to see that there is code being run.

2) Create a custom module, but in your info file make use of the hidden property:


  As of version 7.x, modules and themes may specify that they should not
  be visible on the modules page by adding hidden = TRUE. This is
  commonly used with testing modules used with SimpleTest where
  end-users should never enable the testing modules.