Drupal Includes Files

ROOT/includes/

  - action.inc    -> action engine for executing stored actions

  - ajax.inc      -> function for use with drupal ajax fw

  - archiver.inc  -> classes and interfaces for archiver system

  - authorize.inc -> helper function n form handler for authorize.php

  - batch.inc     -> running process for multiple http request

  - batch.queue.inc   -> queue handlers used by batch API

  - bootstrap.inc -> functions load in every drupal request

  - cache.inc     -> get cache objects for cache bin

  - cache-install.inc -> stub cache used during installation

  - commons.inc   -> many drupal modules reference to this
  - date.inc      -> list of date format and their locals
  - entity.inc    -> interface and entity class
  - errors.inc    -> error handling
  - file.inc      -> handling file upload and server file management
  - file.mimetypes.inc -> mapping mime type with extension
  - form.inc      -> abstract representation of forms
  - graph.inc     -> directed acyclic graph function
  - image.inc     -> image manipulation
  - install.core.inc   -> installing drupal
  - install.inc   ->
  - iso.inc       -> iso for country and language list
  - language.inc  -> multiple language handling
  - locale.inc    -> for locale.module
  - lock.inc      -> database locking mechanism
  - mail.inc      -> processing and sending mail
  - menu.inc      -> drupal menu system
  - module.inc    -> process and load module
  - pager.inc     -> represent database result as page
  - password.inc  -> password hash function for authentication
  - path.inc      -> handling path 
  - registry.inc  -> code registry parser engine
  - session.inc   -> handling user session
  - stream_wrappers.inc  -> handling PHP stream function for file
  - tablesort.inc -> creation of sortable table
  - theme.inc     -> theme system. control output of drupal
  - theme.maintenance.inc -> for maintenance page
  - token.inc     -> placeholder/token replacement system
  - unicode.entities.inc  -> HTML entities
  - unicode.inc   ->
  - update.inc    -> datebase update
  - updater.inc   -> 
  - utility.inc   ->
  - xmlrpc.inc    ->
  - xmlrpcs.inc   -> defining and handling xml-rpc request