PHP SPL

SPL stands for Standard Php Library.

Read all below

• Introduction
• Installing/Configuring
  • Requirements
  • Installation
  • Runtime Configuration
  • Resource Types
• Predefined Constants
• Datastructures
  • SplDoublyLinkedList — The SplDoublyLinkedList class
  • SplStack — The SplStack class
  • SplQueue — The SplQueue class
  • SplHeap — The SplHeap class
  • SplMaxHeap — The SplMaxHeap class
  • SplMinHeap — The SplMinHeap class
  • SplPriorityQueue — The SplPriorityQueue class
  • SplFixedArray — The SplFixedArray class
  • SplObjectStorage — The SplObjectStorage class
• Iterators
  • AppendIterator — The AppendIterator class
  • ArrayIterator — The ArrayIterator class
  • CachingIterator — The CachingIterator class
  • CallbackFilterIterator — The CallbackFilterIterator class
  • DirectoryIterator — The DirectoryIterator class
  • EmptyIterator — The EmptyIterator class
  • FilesystemIterator — The FilesystemIterator class
  • FilterIterator — The FilterIterator class
  • GlobIterator — The GlobIterator class
  • InfiniteIterator — The InfiniteIterator class
  • IteratorIterator — The IteratorIterator class
  • LimitIterator — The LimitIterator class
  • MultipleIterator — The MultipleIterator class
  • NoRewindIterator — The NoRewindIterator class
  • ParentIterator — The ParentIterator class
  • RecursiveArrayIterator — The RecursiveArrayIterator class
  • RecursiveCachingIterator — The RecursiveCachingIterator class
  • RecursiveCallbackFilterIterator — The RecursiveCallbackFilterIterator class
  • RecursiveDirectoryIterator — The RecursiveDirectoryIterator class
  • RecursiveFilterIterator — The RecursiveFilterIterator class
  • RecursiveIteratorIterator — The RecursiveIteratorIterator class
  • RecursiveRegexIterator — The RecursiveRegexIterator class
  • RecursiveTreeIterator — The RecursiveTreeIterator class
  • RegexIterator — The RegexIterator class
• Interfaces
  • Countable — The Countable interface
  • OuterIterator — The OuterIterator interface
  • RecursiveIterator — The RecursiveIterator interface
  • SeekableIterator — The SeekableIterator interface
• Exceptions
  • BadFunctionCallException — The BadFunctionCallException class
  • BadMethodCallException — The BadMethodCallException class
  • DomainException — The DomainException class
  • InvalidArgumentException — The InvalidArgumentException class
  • LengthException — The LengthException class
  • LogicException — The LogicException class
  • OutOfBoundsException — The OutOfBoundsException class
  • OutOfRangeException — The OutOfRangeException class
  • OverflowException — The OverflowException class
  • RangeException — The RangeException class
  • RuntimeException — The RuntimeException class
  • UnderflowException — The UnderflowException class
  • UnexpectedValueException — The UnexpectedValueException class
• SPL Functions
  • class_implements — Return the interfaces which are implemented by the given class
  • class_parents — Return the parent classes of the given class
  • class_uses — Return the traits used by the given class
  • iterator_apply — Call a function for every element in an iterator
  • iterator_count — Count the elements in an iterator
  • iterator_to_array — Copy the iterator into an array
  • spl_autoload_call — Try all registered __autoload() function to load the requested class
  • spl_autoload_extensions — Register and return default file extensions for spl_autoload
  • spl_autoload_functions — Return all registered __autoload() functions
  • spl_autoload_register — Register given function as __autoload() implementation
  • spl_autoload_unregister — Unregister given function as __autoload() implementation
  • spl_autoload — Default implementation for __autoload()
  • spl_classes — Return available SPL classes
  • spl_object_hash — Return hash id for given object
• File Handling
  • SplFileInfo — The SplFileInfo class
  • SplFileObject — The SplFileObject class
  • SplTempFileObject — The SplTempFileObject class
• Miscellaneous Classes and Interfaces
• ArrayObject — The ArrayObject class
• SplObserver — The SplObserver interface
• SplSubject — The SplSubject interface

For ArrayObject, Read below:
http://php.net/manual/en/class.arrayobject.php