Add lots of documentation.

git-svn-id: http://htmlpurifier.org/svnroot/htmlpurifier/trunk@293 48356398-32a2-884e-a903-53898d9a118a

library/HTMLPurifier/AttrContext.php

@@ -5,10 +5,21 @@
  * 
  * All it is is a data-structure that holds objects that accumulate state, like
  * HTMLPurifier_IDAccumulator.
+ * 
+ * @param Many functions that accept this object have it as a mandatory
+ *        parameter, even when there is no use for it.  Though this is
+ *        for the same reasons as why HTMLPurifier_Config is a mandatory
+ *        parameter, it is also because you cannot assign a default value
+ *        to a parameter passed by reference (passing by reference is essential
+ *        for context to work in PHP 4).
  */
 
 class HTMLPurifier_AttrContext
 {
+    /**
+     * Contains an HTMLPurifier_IDAccumulator, which keeps track of used IDs.
+     * @public
+     */
     var $id_accumulator;
 }