Add option to sort attributes in HTML output.

src/main/java/org/jsoup/nodes/Attributes.java

@@ -20,6 +20,7 @@
 import java.util.Map;
 import java.util.NoSuchElementException;
 import java.util.Set;
+import java.util.stream.IntStream;
 
 import static org.jsoup.internal.Normalizer.lowerCase;
 import static org.jsoup.internal.SharedConstants.AttrRangeKey;
@@ -465,13 +466,29 @@ public String html() {
     }
 
     final void html(final Appendable accum, final Document.OutputSettings out) throws IOException {
-        final int sz = size;
-        for (int i = 0; i < sz; i++) {
-            if (isInternalKey(keys[i]))
-                continue;
-            final String key = Attribute.getValidKey(keys[i], out.syntax());
-            if (key != null)
-                Attribute.htmlNoValidate(key, (String) vals[i], accum.append(' '), out);
+        if (out.sortAttributes()) {
+            IntStream.range(0, keys.length)
+                    .limit(size)
+                    .filter(i -> !isInternalKey(keys[i])
+                            && Attribute.getValidKey(keys[i], out.syntax()) != null)
+                    .mapToObj(Integer::valueOf)
+                    .sorted((a, b) -> keys[a].compareTo(keys[b]))
+                    .forEachOrdered(i -> {
+                        try {
+                            Attribute.htmlNoValidate(keys[i], (String) vals[i], accum.append(' '), out);
+                        } catch (IOException e) {
+                            throw new RuntimeException(e);
+                        }
+                    });
+        } else {
+            final int sz = size;
+            for (int i = 0; i < sz; i++) {
+                if (isInternalKey(keys[i]))
+                    continue;
+                final String key = Attribute.getValidKey(keys[i], out.syntax());
+                if (key != null)
+                    Attribute.htmlNoValidate(key, (String) vals[i], accum.append(' '), out);
+            }
         }
     }
 

src/main/java/org/jsoup/nodes/Document.java

@@ -5,12 +5,8 @@
 import org.jsoup.helper.DataUtil;
 import org.jsoup.helper.Validate;
 import org.jsoup.internal.StringUtil;
-import org.jsoup.parser.ParseSettings;
-import org.jsoup.parser.Parser;
-import org.jsoup.parser.Tag;
-import org.jsoup.select.Elements;
-import org.jsoup.select.Evaluator;
-import org.jsoup.select.Selector;
+import org.jsoup.parser.*;
+import org.jsoup.select.*;
 import org.jspecify.annotations.Nullable;
 
 import java.nio.charset.Charset;
@@ -403,6 +399,7 @@ public enum Syntax {html, xml}
 
         private boolean prettyPrint = true;
         private boolean outline = false;
+        private boolean sortAttributes = false;
         private int indentAmount = 1;
         private int maxPaddingWidth = 30;
         private Syntax syntax = Syntax.html;
@@ -520,7 +517,25 @@ public OutputSettings prettyPrint(boolean pretty) {
             prettyPrint = pretty;
             return this;
         }
-
+
+        /**
+         * Get if attribute sorting is enabled. Default is false. If enabled, attributes will be sorted by name
+         * @return if attribute sorting is enabled.
+         */
+        public boolean sortAttributes() {
+            return sortAttributes;
+        }
+
+        /**
+         * Enable or disable attribute sorting.
+         * @param sort new attribute sorting setting
+         * @return this, for chaining
+         */
+        public OutputSettings sortAttributes(boolean sort) {
+            sortAttributes = sort;
+            return this;
+        }
+
         /**
          * Get if outline mode is enabled. Default is false. If enabled, the HTML output methods will consider
          * all tags as block.

src/test/java/org/jsoup/nodes/ElementTest.java

@@ -468,6 +468,14 @@ public void testOuterHtml() {
             TextUtil.stripNewlines(doc.outerHtml()));
     }
 
+    @Test
+    public void testOuterHtmlWithSortedAttributes() {
+        Document doc = Jsoup.parse("<p style='margin: 0' id='hello'>Hello</p>");
+        doc.outputSettings().sortAttributes(true);
+        assertEquals("<html><head></head><body><p id=\"hello\" style=\"margin: 0\">Hello</p></body></html>",
+                TextUtil.stripNewlines(doc.outerHtml()));
+    }
+
     @Test
     public void testInnerHtml() {
         Document doc = Jsoup.parse("<div>\n <p>Hello</p> </div>");