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:
Functions and methods should be named using the "studly caps" style (also referred to as "bumpy case" or "camel caps"). Functions should in addition 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. Some examples:
Private class members (meaning class members that are intented 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:
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. For example, the constants used by the DB:: package all begin with DB_.
If your package needs to define global variables, their name 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.