<?php 
/*
As I found the sort() function normally works as ascending order based on the following priority :
1. NULL
2. Empty 
3. Boolean FALSE 
4. String 
5. Float 
6. Int 
7. Array
8. Object 

Consider the following array: 
*/

$a = ['fruit'=> 'apple', 'A' => 10, 20, 5, 2.5, 5=>'A new value', 'last' => 'value', TRUE, NULL, "", FALSE, array(), new StdClass];
sort($a);
var_dump($a);

#The output is: 

array(13) {
  [0]=>NULL
  [1]=> string(0) ""
  [2]=>bool(false)
  [3]=>string(11) "A new value"
  [4]=>string(5) "apple"
  [5]=>string(5) "value"
  [6]=> float(2.5)
  [7]=> int(5)
  [8]=>int(10)
  [9]=>int(20)
  [10]=>array(0) { }
  [11]=> bool(true)
  [12]=>object(stdClass)#1 (0) {}
}

//Hope it will remove your confusion when you're sorting an array with mix type data. 
?>