PHP variables start with the $ sign followed by the variable name.
A valid variable name starts with a letter or an underscore followed by any combination of letters, numbers, and/or underscores.
Variable name is case sensitive.
<?php $_some_value = 'abc'; // valid $1number = 12.3; // not valid! $some$signs% = '&^%'; // not valid! $My_2_home = "ok"; // valid $My_2_Home = 'no'; // this is a different variable $isThisCamelCase = true; // camel case ?>
Everything after // is a comment, and is thus ignored by PHP.
Variable names like $_some_value and $My_2_home are valid.
$1number is not valid as it starts with number.
$some$signs% are not valid as it contains invalid symbols.
$My_2_home and $My_2_Home are two different variables.