 #2.
~~~~~

~~~~~
.     ,  -   PHP     .      .     ,     - my_variable. ? .     ,       .     ,     ,   : " -  ". :     ,    my_variable      " -  ".       PHP-.
,     "my_variable" (    " "),      " -  ".    PHP-:
<?php
//    
/*
 PHP,   

*/
#    
$my_variable = " -  ";
echo $my_variable;
// 
?>
   ,      $. ,     .    (""),      .
    PHP,    ,    ,      " -  ".  echo $my_variable;     .        " -  ".
.   ,      -  .   ,          .
~~~~~
  .
         . :
<?php
$a1 = 5;
$a2 = $a1 - 4;
echo $a2;
?>
       $a1  5,   $a2   $a1   4.          1,   5-4=1.
   :
1.      ,   ,    . 
$userName -  
$m -  
$user-Name -  
$this_is_my_good_variable_userName -  
2.       , ,    "_".
3.          .
~~~~~
  .  .