PHP: Rules - Manual

Rules

The following list gives an overview of which rights the PHP project reserves for itself, when choosing names for new internal identifiers. The definitive guide is the official » CODING STANDARDS:

PHP owns the top-level namespace but tries to find decent descriptive names and avoid any obvious clashes.
Function names use underscores between words, while class names use both the camelCase and PascalCase rules.
PHP will prefix any global symbols of an extension with the name of the extension. (In the past, there have been numerous exceptions to this rule.) Examples:
- curl_close()
- mysql_query()
- PREG_SPLIT_DELIM_CAPTURE
- new DOMDocument()
- strpos() (example of a past mistake)
- new SplFileObject()
Iterators and Exceptions are however simply postfixed with "Iterator" and "Exception." Examples:
- ArrayIterator
- LogicException
PHP reserves all symbols starting with __ as magical. It is recommended that you do not create symbols starting with __ in PHP unless you want to use documented magical functionality. Examples:
- __get()
- __autoload()

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User Contributed Notes 1 note

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Anonymous ¶

4 years ago


#### Rules for PHP identifiers

1. A variable starts with the $ sign, followed by the name of the variable.

2. A variable name must start with a letter or the underscore character.

3. A variable name can only contain alpha-numeric characters and underscores (A-z, 0-9, and _ ).

4. Identifiers are case sensitive. Therefore, a variable named $unicorn is different from a variable named $Unicorn, $uNicOrn, or $unicorN. 

5. Identifiers can be any length.

6. An identifier name can’t be identical to any of PHP’s predefined keywords.

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