function internal( x, searchElement, fromIndex ) {
	var i;
	for ( i = fromIndex; i >= 0; i-- ) {
		if ( searchElement === x[ i ] ) {
			return i;
		}
	}
	return -1;
}
Returns the index of the last element which equals a provided search element.

@private
@param {Collection} x - input array
@param {*} searchElement - search element
@param {NonNegativeInteger} fromIndex - starting index (inclusive)
@returns {integer} index

@example
var x = [ 1, 2, 3, 4 ];

var idx = internal( x, 2, 3 );
// returns 1