Start on validating config

lib/AbstractSanitizer.php

@@ -399,7 +399,7 @@ abstract class AbstractSanitizer {
      * - `name`: The localName of the element
      * - `namespace`: The namespaceURI of the element, a string or null. If omitted the HTML namespace is assumed
      * 
-     * The entries in attribute lists are arrays with the follwoing keys
+     * The entries in attribute lists are arrays with the following keys
      * 
      * - `name`: The localName of the attribute
      * - `namespace`: The namespaceURI of the attribute. If omitted the null namespace is assumed
@@ -408,5 +408,14 @@ abstract class AbstractSanitizer {
      * @param array $config A configuration to use instead of the default one
      */
     public function __construct(array $config = null) {
+        if ($config === null) {
+            // use the default configuration if none is specified
+            $this->config = self::DEFAULT_CONF;
+        } else {
+            // otherwise validate the configuration; the specification provides
+            //   no clue is to what happens when the configuration is invalid,
+            //   so we'll just have to do our best
+            $conf = [];
+        }
     }
 }