(PHP 5, PHP 7, PHP 8)
       The number of nodes in the list. The range of valid child node 
       indices is 0 to length - 1 inclusive.
      
| Version | Description | 
|---|---|
| 8.0.0 | DOMNodeList implements IteratorAggregate now. Previously, Traversable was implemented instead. | 
| 7.2.0 | The Countable interface is implemented and returns the value of the length property. |