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()