1. If the require well-formed flag is set (its value is true), and this node's localName attribute contains the character ":" (U+003A COLON) or does not match the XML Name production, then throw an exception; the serialization of this node would not be a well-formed element.
2. Let markup be the string "<" (U+003C LESS-THAN SIGN).
3. Let qualified name be an empty string.
4. Let skip end tag be a boolean flag with value false.
5. Let ignore namespace definition attribute be a boolean flag with value false.
6. Given prefix map, copy a namespace prefix map and let map be the result.
7. Let local prefixes map be an empty map. The map has unique Node prefix strings as its keys, with corresponding namespaceURI Node values as the map's key values (in this map, the null namespace is represented by the empty string).
   Note

   This map is local to each element. It is used to ensure there are no conflicting prefixes should a new namespace prefix attribute need to be generated. It is also used to enable skipping of duplicate prefix definitions when writing an element's attributes: the map allows the algorithm to distinguish between a prefix in the namespace prefix map that might be locally-defined (to the current Element) and one that is not.

8. Let local default namespace be the result of recording the namespace information for node given map and local prefixes map.
   Note

   The above step will update map with any found namespace prefix definitions, add the found prefix definitions to the local prefixes map and return a local default namespace value defined by a default namespace attribute if one exists. Otherwise it returns null.

9. Let inherited ns be a copy of namespace.
10. Let ns be the value of node's namespaceURI attribute.
11. If inherited ns is equal to ns, then:
    1. If local default namespace is not null, then set ignore namespace definition attribute to true.
    2. If ns is the XML namespace, then append to qualified name the concatenation of the string "xml:" and the value of node's localName.
    3. Otherwise, append to qualified name the value of node's localName. The node's prefix if it exists, is dropped.
    4. Append the value of qualified name to markup.
12. Otherwise, inherited ns is not equal to ns (the node's own namespace is different from the context namespace of its parent). Run these sub-steps:
    1. Let prefix be the value of node's prefix attribute.
    2. Let candidate prefix be the result of retrieving a preferred prefix string prefix from map given namespace ns.
       Note

       The above may return null if no namespace key ns exists in map.

    3. If the value of prefix matches "xmlns", then run the following steps:
       1. If the require well-formed flag is set, then throw an error. An Element with prefix "xmlns" will not legally round-trip in a conforming XML parser.
       2. Let candidate prefix be the value of prefix.
    4. Found a suitable namespace prefix: if candidate prefix is not null (a namespace prefix is defined which maps to ns), then:
       Note

       The following may serialize a different prefix than the Element's existing prefix if it already had one. However, the retrieving a preferred prefix string algorithm already tried to match the existing prefix if possible.

       1. Append to qualified name the concatenation of candidate prefix, ":" (U+003A COLON), and node's localName. There exists on this node or the node's ancestry a namespace prefix definition that defines the node's namespace.
       2. If the local default namespace is not null (there exists a locally-defined default namespace declaration attribute) and its value is not the XML namespace, then let inherited ns get the value of local default namespace unless the local default namespace is the empty string in which case let it get null (the context namespace is changed to the declared default, rather than this node's own namespace).
          Note

          Any default namespace definitions or namespace prefixes that define the XML namespace are omitted when serializing this node's attributes.

       3. Append the value of qualified name to markup.
    5. Otherwise, if prefix is not null, then:
       Note

       By this step, there is no namespace or prefix mapping declaration in this node (or any parent node visited by this algorithm) that defines prefix otherwise the step labelled Found a suitable namespace prefix would have been followed. The sub-steps that follow will create a new namespace prefix declaration for prefix and ensure that prefix does not conflict with an existing namespace prefix declaration of the same localName in node's attribute list.

       1. If the local prefixes map contains a key matching prefix, then let prefix be the result of generating a prefix providing as input map, ns, and prefix index.
       2. Add prefix to map given namespace ns.
       3. Append to qualified name the concatenation of prefix, ":" (U+003A COLON), and node's localName.
       4. Append the value of qualified name to markup.
       5. Append the following to markup, in the order listed:
          Note

          The following serializes a namespace prefix declaration for prefix which was just added to the map.

          1. " " (U+0020 SPACE);
          2. The string "xmlns:";
          3. The value of prefix;
          4. "="" (U+003D EQUALS SIGN, U+0022 QUOTATION MARK);
          5. The result of serializing an attribute value given ns and the require well-formed flag as input;
          6. """ (U+0022 QUOTATION MARK).
          7. If local default namespace is not null (there exists a locally-defined default namespace declaration attribute), then let inherited ns get the value of local default namespace unless the local default namespace is the empty string in which case let it get null.
    6. Otherwise, if local default namespace is null, or local default namespace is not null and its value is not equal to ns, then:
       Note

       At this point, the namespace for this node still needs to be serialized, but there's no prefix (or candidate prefix) availble; the following uses the default namespace declaration to define the namespace--optionally replacing an existing default declaration if present.

       1. Set the ignore namespace definition attribute flag to true.
       2. Append to qualified name the value of node's localName.
       3. Let the value of inherited ns be ns.
          Note

          The new default namespace will be used in the serialization to define this node's namespace and act as the context namespace for its children.

       4. Append the value of qualified name to markup.
       5. Append the following to markup, in the order listed:
          Note

          The following serializes the new (or replacement) default namespace definition.

          1. " " (U+0020 SPACE);
          2. The string "xmlns";
          3. "="" (U+003D EQUALS SIGN, U+0022 QUOTATION MARK);
          4. The result of serializing an attribute value given ns and the require well-formed flag as input;
          5. """ (U+0022 QUOTATION MARK).
    7. Otherwise, the node has a local default namespace that matches ns. Append to qualified name the value of node's localName, let the value of inherited ns be ns, and append the value of qualified name to markup.
       Note

       All of the combinations where ns is not equal to inherited ns are handled above such that node will be serialized preserving its original namespaceURI.

13. Append to markup the result of the XML serialization of node's attributes given map, prefix index, local prefixes map, ignore namespace definition attribute flag, and require well-formed flag.
14. If ns is the HTML namespace, and the node's list of children is empty, and the node's localName matches any one of the following void elements: "area", "base", "basefont", "bgsound", "br", "col", "embed", "frame", "hr", "img", "input", "keygen", "link", "menuitem", "meta", "param", "source", "track", "wbr"; then append the following to markup, in the order listed:
    1. " " (U+0020 SPACE);
    2. "/" (U+002F SOLIDUS).
    and set the skip end tag flag to true.
15. If ns is not the HTML namespace, and the node's list of children is empty, then append "/" (U+002F SOLIDUS) to markup and set the skip end tag flag to true.
16. Append ">" (U+003E GREATER-THAN SIGN) to markup.
17. If the value of skip end tag is true, then return the value of markup and skip the remaining steps. The node is a leaf-node.
18. If ns is the HTML namespace, and the node's localName matches the string "template", then this is a template element. Append to markup the result of XML serializing a DocumentFragment node given the template element's template contents (a DocumentFragment), providing inherited ns, map, prefix index, and the require well-formed flag.
    Note

    This allows template content to round-trip , given the rules for parsing XHTML documents.

19. Otherwise, append to markup the result of running the XML serialization algorithm on each of node's children, in tree order, providing inherited ns, map, prefix index, and the require well-formed flag.
20. Append the following to markup, in the order listed:
    1. "</" (U+003C LESS-THAN SIGN, U+002F SOLIDUS);
    2. The value of qualified name;
    3. ">" (U+003E GREATER-THAN SIGN).
21. Return the value of markup.

If the require well-formed flag is set (its value is true), and this node has no documentElement (the documentElement attribute's value is null), then throw an exception; the serialization of this node would not be a well-formed document.

Otherwise, run the following steps:

1. Let serialized document be an empty string.
2. For each child child of node, in tree order, run the XML serialization algorithm on the child passing along the provided arguments, and append the result to serialized document.
   Note

   This will serialize any number of ProcessingInstruction and Comment nodes both before and after the Document's documentElement node, including at most one DocumentType node. (Text nodes are not allowed as children of the Document.)

3. Return the value of serialized document.

If the require well-formed flag is set (its value is true), and node's data contains characters that are not matched by the XML Char production or contains "--" (two adjacent U+002D HYPHEN-MINUS characters) or that ends with a "-" (U+002D HYPHEN-MINUS) character, then throw an exception; the serialization of this node's data would not be well-formed.

Otherwise, return the concatenation of "<!--", node's data, and "-->".

1. If the require well-formed flag is set (its value is true), and node's data contains characters that are not matched by the XML Char production, then throw an exception; the serialization of this node's data would not be well-formed.
2. Let markup be the value of node's data.
3. Replace any occurrences of "&" in markup by "&".
4. Replace any occurrences of "<" in markup by "<".
5. Replace any occurrences of ">" in markup by ">".
6. Return the value of markup.

1. Let markup the empty string.
2. For each child child of node, in tree order, run the XML serialization algorithm on the child given namespace, prefix map, a reference to prefix index, and flag require well-formed. Concatenate the result to markup.
3. Return the value of markup.

1. If the require well-formed flag is true and the node's publicId attribute contains characters that are not matched by the XML PubidChar production, then throw an exception; the serialization of this node would not be a well-formed document type declaration.
2. If the require well-formed flag is true and the node's systemId attribute contains characters that are not matched by the XML Char production or that contains both a """ (U+0022 QUOTATION MARK) and a "'" (U+0027 APOSTROPHE), then throw an exception; the serialization of this node would not be a well-formed document type declaration.
3. Let markup be an empty string.
4. Append the string "<!DOCTYPE" to markup.
5. Append " " (U+0020 SPACE) to markup.
6. Append the value of the node's name attribute to markup. For a node belonging to an HTML document, the value will be all lowercase.
7. If the node's publicId is not the empty string then append the following, in the order listed, to markup:
   1. " " (U+0020 SPACE);
   2. The string "PUBLIC";
   3. " " (U+0020 SPACE);
   4. """ (U+0022 QUOTATION MARK);
   5. The value of the node's publicId attribute;
   6. """ (U+0022 QUOTATION MARK).
8. If the node's systemId is not the empty string and the node's publicId is set to the empty string, then append the following, in the order listed, to markup:
   1. " " (U+0020 SPACE);
   2. The string "SYSTEM".
9. If the node's systemId is not the empty string then append the following, in the order listed, to markup:
   1. " " (U+0020 SPACE);
   2. """ (U+0022 QUOTATION MARK);
   3. The value of the node's systemId attribute;
   4. """ (U+0022 QUOTATION MARK).
10. Append ">" (U+003E GREATER-THAN SIGN) to markup.
11. Return the value of markup.

1. If the require well-formed flag is set (its value is true), and node's target contains a ":" (U+003A COLON) character or is an ASCII case-insensitive match for the string "xml", then throw an exception; the serialization of this node's target would not be well-formed.
2. If the require well-formed flag is set (its value is true), and node's data contains characters that are not matched by the XML Char production or contains the string "?>" (U+003F QUESTION MARK, U+003E GREATER-THAN SIGN), then throw an exception; the serialization of this node's data would not be well-formed.
3. Let markup be the concatenation of the following, in the order listed:
   1. "<?" (U+003C LESS-THAN SIGN, U+003F QUESTION MARK);
   2. The value of node's target;
   3. " " (U+0020 SPACE);
   4. The value of node's data;
   5. "?>" (U+003F QUESTION MARK, U+003E GREATER-THAN SIGN).
4. Return the value of markup.