How to declare variable in php.

1. Start with a "$"
2. Followed by letter or underscore
3. Can contain letters, numbers, underscores or dashes
4. No spaces
5. Case sensitive

Example : Variable names

$item
$Item
$myVariable
$this_variable
$this-variable
$product1
$_book
$__bookPage

But, I recommend that do not use these from the above variable declaration
$this-variable,
$_book - Because php uses _ sign internally for many things
$__bookPage