PHP4 User Manual: Variables-Basics_PHP Tutorial

Chapter 7. Variable Directory List Website Construction Server Script Class PHPPHP User Manual fancylanguage.variables.html#language.variables.basics>Basics Fixed Variables Variables Scope Variables Variables Outside PHP Basics
Description of Variables: In PHP is a dollar sign followed by the name of the variable. Variable names are case-sensitive.
The naming of variable names is consistent with other tags in PHP. A valid variable name begins with a word line or underscore, followed by some words, numbers, or underscores. Treated as a regular expression, it would look like this: [a-zA-Z_x7f-xff][a-zA-Z0-9_x7f-xff]*
Note: A letter is a-z, A-Z, and the ASCII character 127 through 255 (0x7f-0xff).
$var = "Bob";$Var = "Joe";echo "$var, $Var"; // Output "Bob, Joe"$4site = not yet; // Error; cannot start with a number $_4site = not yet; // Valid; can start with an underscore $täyte = mansikka; // Valid: ä is ASCII 228.

In PHP 3, variables are assigned by of. In other words, when you assign an expression to a variable, the value of the original expression is copied to the destination variable.
This means that assigning the value of one variable to another variable only changes the value of those variables without affecting the other variables. See Expressions for more information.
PHP 4 provides another way to assign values ​​to variables: reference assignment. This means that the new variable simply references the original variable (the new variable is just a "pseudonym" or "pointer") and changes to the new variable will affect the original variable and vice versa. This also means that no copying is performed: therefore, allocations are faster. However, such speedups only apply to complex loops or allocating large arrays and objects.
To assign a reference, just add an "&" sign before the variable to which it is assigned (source variable). For example, the following code snippet prints My name is Bob twice:

An important note: only one of the specified variables can be assigned by reference.