Naming

The classes in this library follow a few naming conventions, which may
help you find the correct functionality more quickly.  Here they are:

All classes occupy the HTMLPurifier pseudo-namespace.
    This means that all classes are prefixed with HTMLPurifier_.  As such, all
    names under HTMLPurifier_ are reserved.  I recommend that you use the name
    HTMLPurifierX_YourName_ClassName, especially if you want to take advantage
    of HTMLPurifier_ConfigDef.

All classes correspond to their path if library/ was in the include path
    HTMLPurifier_AttrDef is located at HTMLPurifier/AttrDef.php; replace
    underscores with slashes and append .php and you'll have the location of
    the class.

Harness and Test are reserved class names for unit tests
    The suffix "Test" indicates that the class is a subclass of UnitTestCase
    (of the Simpletest library) and is testable. "Harness" indicates a subclass
    of UnitTestCase that is not meant to be run but to be extended into 
    concrete test cases and contains custom test methods (i.e. assert*())

Class names do not necessarily represent inheritance hierarchies
    While we try to reflect inheritance in naming to some extent, it is not
    guaranteed (for instance, none of the classes inherit from HTMLPurifier,
    the base class).  However, all class files have the require_once
    declarations to whichever classes they are tightly coupled to.

Strategy has a meaning different from the Gang of Four pattern
    In Design Patterns, the Gang of Four describes a Strategy object as
    encapsulating an algorithm so that they can be switched at run-time.  While
    our strategies are indeed algorithms, they are not meant to be substituted:
    all must be present in order for proper functioning.

Abbreviations are avoided
    We try to avoid abbreviations as much as possible, but in some cases, 
    abbreviated version is more readable than the full version. Here, we
    list common abbreviations:
        Attr(s) -> Attribute(s)
        Def -> Definition

Ambiguity concerning the definition of Def/Definition
    While a definition normally defines the structure/acceptable values of
    an entity, most of the definitions in this application also attempt
    to validate and fix the value.  I am unsure of a better name, as
    "Validator" would exclude fixing the value, "Fixer" doesn't invoke
    the proper image of "fixing" something, and "ValidatorFixer" is too long!
    Some other suggestions were "Handler", "Reference", "Check", "Fix",
    "Repair" and "Heal".

Transform not Transformer
    Transform is both a noun and a verb, and thus we define a "Transform" as
    something that "transforms," leaving "Transformer" (which sounds like an
    electrical device/robot toy).