Variable names:

Variable names:
Variable names always begin with a dollar sign ($) and are case-sensitive.
 Here are some valid variable names:
$bill
$head_count
 $MaximumForce
 $I_HEART_PHP
$_underscore
$_int
Here are some illegal variable names:
$not valid
$| $3wa
These variables are all different:
$hot_stuff  $Hot_stuff  $hot_Stuff  $HOT_STUFF