Add method to rename an Element's Tag without resetting the tag's properties

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

@@ -177,6 +177,20 @@ public Element tagName(String tagName) {
         return this;
     }
 
+    /**
+     * Change (rename) the tag of this element. For example, convert a {@code <span>} to a {@code <div>} with
+     * {@code el.tagName("div");}.
+     *
+     * @param tagName new tag name for this element
+     * @return this element, for chaining
+     * @see Elements#tagName(String)
+     */
+    public Element renameTagPreserveProperties(String tagName) {
+        Validate.notEmptyParam(tagName, "tagName");
+        tag = Tag.convertTag(tag, tagName); // maintains the case option of the original parse
+        return this;
+    }
+
     /**
      * Get the Tag for this element.
      *

src/main/java/org/jsoup/parser/Tag.java

@@ -78,6 +78,26 @@ public static Tag valueOf(String tagName, ParseSettings settings) {
         return tag;
     }
 
+    /**
+     * Create a new tag with a new name, copying the same characteristics as the old one.
+     *
+     * @param tagName Name of tag, e.g. "p". Case insensitive.
+     * @return The tag, either defined or new generic.
+     */
+    public static Tag convertTag(Tag oldTag, String tagName) {
+        Validate.notNull(tagName);
+        Tag tag = new Tag(tagName);
+        tag.empty = oldTag.empty;
+        tag.formList = oldTag.formList;
+        tag.formSubmit = oldTag.formSubmit;
+        tag.formatAsBlock = oldTag.formatAsBlock;
+        tag.isBlock = oldTag.isBlock;
+        tag.preserveWhitespace = oldTag.preserveWhitespace;
+        tag.selfClosing = oldTag.selfClosing;
+
+        return tag;
+    }
+
     /**
      * Get a Tag by name. If not previously defined (unknown), returns a new generic tag, that can do anything.
      * <p>

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

@@ -1016,6 +1016,39 @@ public void testTagNameSet() {
         assertEquals("<em>Hello</em>", doc.select("div").first().html());
     }
 
+    @Test
+    public void tagNameChangeResetsProperties() {
+        Document doc = Jsoup.parse("<img src='foo.png'>");
+        Element img = doc.select("img").first();
+
+        assertTrue(img.tag().isInline());
+        assertTrue(img.tag().isSelfClosing());
+        assertFalse(img.isBlock());
+
+        // When we rename a tag to a new, unregistered name, confirm that its properties are reset, just as if
+        // we had created one from scratch.
+
+        Tag testTag = Tag.valueOf("jspControl:image", NodeUtils.parser(doc).settings());
+        img.tagName("jspControl:image");
+        assertEquals(testTag, img.tag());
+    }
+
+    @Test
+    public void testRenameTagPreserveProperties() {
+        Document doc = Jsoup.parse("<img src='foo.png'>");
+        Element img = doc.select("img").first();
+        assertTrue(img.tag().isInline());
+        assertTrue(img.tag().isSelfClosing());
+        assertFalse(img.isBlock());
+
+        // When we rename to an unrecognized tag, but tell the element to keep its tag properties, the previous
+        // assertions should still hold true.
+        img.renameTagPreserveProperties("jspControl:image");
+        assertTrue(img.tag().isInline());
+        assertTrue(img.tag().isSelfClosing());
+        assertFalse(img.isBlock());
+    }
+
     @Test
     public void testHtmlContainsOuter() {
         Document doc = Jsoup.parse("<title>Check</title> <div>Hello there</div>");