code: function(value, equals)
    {
      var equality = equals || equalsStrict;
  
      for (var i = 0; i < this.length; i++)
      {
        if ( equality( value, this[ i ] ) )
        {
          return i;
        }
      }
  
      return -1;
    }
docs: Returns the index of the given element in this collection or returns -1
  if the element doesn't exist in this collection.
  
  ```javascript
  var c = Rekord.collect(1, 2, 3, 4);
  c.indexOf( 1 ); // 0
  c.indexOf( 2 ); // 1
  c.indexOf( 5 ); // -1
  ```
  
  @method
  @memberof Rekord.Collection#
  @param {Any} value -
  The value to search for.
  @param {equalityCallback} [equals=Rekord.equalsStrict] -
  The function which determines whether one of the elements that exist in
  this collection are equivalent to the given value.
  @return {Number} -
  The index of the element in this collection or -1 if it was not found.
  @see Rekord.equals
  @see Rekord.equalsStrict