[DOXIA-734] Restore handling of XHTML 1.0 obsolete attributes

doxia-core/src/main/java/org/apache/maven/doxia/parser/AbstractXmlParser.java

@@ -379,11 +379,14 @@ protected void handleEntity(XmlPullParser parser, Sink sink) throws XmlPullParse
      * method.
      */
     protected void handleUnknown(XmlPullParser parser, Sink sink, int type) {
-        Object[] required = new Object[] {type};
-
         SinkEventAttributeSet attribs = getAttributesFromParser(parser);
 
-        sink.unknown(parser.getName(), required, attribs);
+        handleUnknown(parser.getName(), attribs, sink, type);
+    }
+
+    protected void handleUnknown(String elementName, SinkEventAttributeSet attribs, Sink sink, int type) {
+        Object[] required = new Object[] {type};
+        sink.unknown(elementName, required, attribs);
     }
 
     /**

doxia-core/src/main/java/org/apache/maven/doxia/parser/Xhtml1BaseParser.java

@@ -0,0 +1,97 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.maven.doxia.parser;
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.function.Function;
+
+import org.apache.maven.doxia.sink.Sink;
+import org.apache.maven.doxia.sink.impl.SinkEventAttributeSet;
+import org.codehaus.plexus.util.xml.pull.XmlPullParser;
+
+/**
+ * Acts as bridge between legacy parsers relying on <a href="https://www.w3.org/TR/xhtml1/">XHTML 1.0 Transitional (based on HTML4.0.1)</a>
+ * and the {@link Xhtml5BaseParser} only supporting HTML5 elements/attributes.
+ *
+ * Adds support for elements/attributes which <a href="https://html.spec.whatwg.org/#non-conforming-features">became obsolete in HTML5</a> but are
+ * commonly used for XDoc/FML.
+ *
+ * @see <a href="https://www.w3.org/TR/html5-diff/">HTML5 Differences from HTML4</a>.
+ */
+public class Xhtml1BaseParser extends Xhtml5BaseParser {
+
+    private static final class AttributeMapping {
+        private final String sourceName;
+        private final String targetName;
+        private final Function<String, String> valueMapper;
+
+        AttributeMapping(String sourceAttribute, String targetAttribute) {
+            this(sourceAttribute, targetAttribute, Function.identity());
+        }
+
+        AttributeMapping(String sourceName, String targetName, Function<String, String> valueMapper) {
+            super();
+            this.sourceName = sourceName;
+            this.targetName = targetName;
+            this.valueMapper = valueMapper;
+        }
+
+        public String getSourceName() {
+            return sourceName;
+        }
+
+        public String getTargetName() {
+            return targetName;
+        }
+
+        public Function<String, String> getValueMapper() {
+            return valueMapper;
+        }
+    }
+
+    /**
+     * All obsolete attributes in a map with key = affected element name, value = {@link AttributeMapping}
+     */
+    private static final Map<String, AttributeMapping> ATTRIBUTE_MAPPING_TABLE = new HashMap<>();
+
+    static {
+        ATTRIBUTE_MAPPING_TABLE.put("a", new AttributeMapping("name", "id"));
+    }
+
+    /**
+     * Translates obsolete XHTML 1.0 attributes to valid XHTML5 ones before calling the underlying {@link Xhtml5BaseParser}.
+     */
+    @Override
+    protected boolean baseStartTag(XmlPullParser parser, Sink sink) {
+        SinkEventAttributeSet attribs = getAttributesFromParser(parser);
+        String elementName = parser.getName();
+        AttributeMapping attributeMapping = ATTRIBUTE_MAPPING_TABLE.get(elementName);
+        if (attributeMapping != null) {
+            String attributeValue = (String) attribs.getAttribute(attributeMapping.getSourceName());
+            if (attributeValue != null) {
+                attribs.addAttribute(
+                        attributeMapping.getTargetName(),
+                        attributeMapping.getValueMapper().apply(attributeValue));
+                attribs.removeAttribute(attributeMapping.getSourceName());
+            }
+        }
+        return super.baseStartTag(elementName, attribs, sink);
+    }
+}