Handle attribute lists in config

lib/AbstractSanitizer.php

@@ -436,7 +436,7 @@ abstract class AbstractSanitizer {
                                 // only use the namespace if it's a string
                                 $ns = $el['namespace'];
                             } else {
-                                // ignore any other value for the namespace
+                                // ignore any other value for the namespace (this is invalid)
                                 continue;
                             }
                         }
@@ -454,7 +454,71 @@ abstract class AbstractSanitizer {
             }
             // continue with attribute lists
             foreach (["allowAttributes", "dropAttributes"] as $opt) {
-                // TODO
+                if (isset($config[$opt]) && is_array($config[$opt])) {
+                    foreach ($config[$opt] as $attr) {
+                        if (is_array($attr) && strlen($attr['name'] ?? "" && isset($attr['elements']))) {
+                            $name = $attr['name'];
+                            if (!isset($attr['namespace'])) {
+                                // the null namespace is assumed
+                                $ns = self::NULL_NAMESPACE;
+                            } elseif (is_string($attr['namespace'])) {
+                                // only use the namespace if it's a string
+                                $ns = $attr['namespace'];
+                            } else {
+                                // ignore any other value for the namespace (this is invalid)
+                                continue;
+                            }
+                            // now check the list of elements
+                            if ($attr['elements'] === "*") {
+                                // the special string "*" means any element
+                                $list = "*";
+                            } elseif (is_array($attr['elements'])) {
+                                // otherwise the element list is like the element lists handled above
+                                $list = [];
+                                foreach ($attr['elements'] as $el) {
+                                    if (is_string($el) && strlen($el)) {
+                                        // strings are assumed to be in the HTML namespace
+                                        $eNs = self::HTML_NAMESPACE;
+                                        $eName = $el;
+                                    } elseif (is_array($el) && strlen($el['name'] ?? "")) {
+                                        $eName = $el['name'];
+                                        if (!array_key_exists("namespace", $el)) {
+                                            // the namespace key being missing means the HTML namespace
+                                            $eNs = self::HTML_NAMESPACE;
+                                        } elseif (!isset($el['namespace'])) {
+                                            // the null namespace is also possible (but will never match in HTML documents)
+                                            $eNs = self::NULL_NAMESPACE;
+                                        } elseif (is_string($el['namespace'])) {
+                                            // only use the namespace if it's a string
+                                            $eNs = $el['namespace'];
+                                        } else {
+                                            // ignore any other value for the namespace (this is invalid)
+                                            continue;
+                                        }
+                                    }
+                                    // create any structures which might be missing
+                                    if (!isset($list[$eNs])) {
+                                        $list[$eNs] = [];
+                                    }
+                                    // add the element
+                                    $list[$eNs][$eName] = true;
+                                }
+                            } else {
+                                // ignore any other value for the elements list (this is invalid)
+                                continue;
+                            }
+                            // create any structures which might be missing
+                            if (!isset($out[$opt])) {
+                                $out[$opt] = [];
+                            }
+                            if (!isset($out[$opt][$ns])) {
+                                $out[$opt][$ns] = [];
+                            }
+                            // add the attribute
+                            $out[$opt][$ns][$name] = $list;
+                        }
+                    }
+                }
             }
             // finally handle the boolean options
             foreach (["allowCustomElements", "allowUnknownMarkup", "allowComments", "allowProcessingInstructions", "nullNamespaceAsHtml"] as $opt) {