Naming Conventions
Global Variables and Functions
If your package needs to define global variables, their names should start with a single underscore followed by the package name and another underscore. For example, the PEAR package uses a global variable called $_PEAR_destructor_object_list.
Global functions should be named using the "studly caps" style (also referred to as "bumpy case" or "camel caps"). In addition, they should have the package name as a prefix, to avoid name collisions between packages. The initial letter of the name (after the prefix) is lowercase, and each letter that starts a new "word" is capitalized. An example:
Classes
Classes should be given descriptive names. Avoid using abbreviations where possible. Class names should always begin with an uppercase letter. The PEAR class hierarchy is also reflected in the class name, each level of the hierarchy separated with a single underscore. Examples of good class names are:
Class Variables and Methods
Class variables (a.k.a properties) and methods should be named using the "studly caps" style (also referred to as "bumpy case" or "camel caps"). Some examples (these would be "public" members):
Private class members (meaning class members that are intended to be used only from within the same class in which they are declared; PHP does not yet support truly-enforceable private namespaces) are preceded by a single underscore. For example:
Note: The following applies to PHP5.
Constants
Constants should always be all-uppercase, with underscores to separate words. Prefix constant names with the uppercased name of the class/package they are used in. Some examples:
Note: The true, false and null constants are excepted from the all-uppercase rule, and must always be lowercase.