(PHP 5 >= 5.3.0, PHP 7, PHP 8)
MultipleIterator::key — Gets the registered iterator instances
Get the registered iterator instances key() result.
This function is currently not documented; only its argument list is available.
This function has no parameters.
An array of all registered iterator instances.
   A RuntimeException if the iterator is invalid (as of PHP 8.1.0), or
   mode MIT_NEED_ALL is set, and at least one attached iterator is not valid.
  
Calling this method from foreach triggers warning "Illegal type returned".
| Version | Description | 
|---|---|
| 8.1.0 | A RuntimeException is now thrown if
       MultipleIterator::key() is called on an
       invalid iterator.  Previously, falsewas returned. | 
