cpython/Doc/library/xml.etree.elementtree.rst

:mod:`xml.etree.ElementTree` --- The ElementTree XML API
========================================================

.. module:: xml.etree.ElementTree
   :synopsis: Implementation of the ElementTree API.

.. moduleauthor:: Fredrik Lundh <fredrik@pythonware.com>

**Source code:** :source:`Lib/xml/etree/ElementTree.py`

--------------

The :mod:`xml.etree.ElementTree` module implements a simple and efficient API
for parsing and creating XML data.

.. versionchanged:: 3.3
   This module will use a fast implementation whenever available.

.. deprecated:: 3.3
   The :mod:`xml.etree.cElementTree` module is deprecated.


.. warning::

   The :mod:`xml.etree.ElementTree` module is not secure against
   maliciously constructed data.  If you need to parse untrusted or
   unauthenticated data see :ref:`xml-vulnerabilities`.

Tutorial
--------

This is a short tutorial for using :mod:`xml.etree.ElementTree` (``ET`` in
short).  The goal is to demonstrate some of the building blocks and basic
concepts of the module.

XML tree and elements
^^^^^^^^^^^^^^^^^^^^^

XML is an inherently hierarchical data format, and the most natural way to
represent it is with a tree.  ``ET`` has two classes for this purpose -
:class:`ElementTree` represents the whole XML document as a tree, and
:class:`Element` represents a single node in this tree.  Interactions with
the whole document (reading and writing to/from files) are usually done
on the :class:`ElementTree` level.  Interactions with a single XML element
and its sub-elements are done on the :class:`Element` level.

.. _elementtree-parsing-xml:

Parsing XML
^^^^^^^^^^^

We'll be using the following XML document as the sample data for this section:

.. code-block:: xml

   <?xml version="1.0"?>
   <data>
       <country name="Liechtenstein">
           <rank>1</rank>
           <year>2008</year>
           <gdppc>141100</gdppc>
           <neighbor name="Austria" direction="E"/>
           <neighbor name="Switzerland" direction="W"/>
       </country>
       <country name="Singapore">
           <rank>4</rank>
           <year>2011</year>
           <gdppc>59900</gdppc>
           <neighbor name="Malaysia" direction="N"/>
       </country>
       <country name="Panama">
           <rank>68</rank>
           <year>2011</year>
           <gdppc>13600</gdppc>
           <neighbor name="Costa Rica" direction="W"/>
           <neighbor name="Colombia" direction="E"/>
       </country>
   </data>

We can import this data by reading from a file::

   import xml.etree.ElementTree as ET
   tree = ET.parse('country_data.xml')
   root = tree.getroot()

Or directly from a string::

   root = ET.fromstring(country_data_as_string)

:func:`fromstring` parses XML from a string directly into an :class:`Element`,
which is the root element of the parsed tree.  Other parsing functions may
create an :class:`ElementTree`.  Check the documentation to be sure.

As an :class:`Element`, ``root`` has a tag and a dictionary of attributes::

   >>> root.tag
   'data'
   >>> root.attrib
   {}

It also has children nodes over which we can iterate::

   >>> for child in root:
   ...     print(child.tag, child.attrib)
   ...
   country {'name': 'Liechtenstein'}
   country {'name': 'Singapore'}
   country {'name': 'Panama'}

Children are nested, and we can access specific child nodes by index::

   >>> root[0][1].text
   '2008'


.. note::

   Not all elements of the XML input will end up as elements of the
   parsed tree. Currently, this module skips over any XML comments,
   processing instructions, and document type declarations in the
   input. Nevertheless, trees built using this module's API rather
   than parsing from XML text can have comments and processing
   instructions in them; they will be included when generating XML
   output. A document type declaration may be accessed by passing a
   custom :class:`TreeBuilder` instance to the :class:`XMLParser`
   constructor.


.. _elementtree-pull-parsing:

Pull API for non-blocking parsing
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Most parsing functions provided by this module require the whole document
to be read at once before returning any result.  It is possible to use an
:class:`XMLParser` and feed data into it incrementally, but it is a push API that
calls methods on a callback target, which is too low-level and inconvenient for
most needs.  Sometimes what the user really wants is to be able to parse XML
incrementally, without blocking operations, while enjoying the convenience of
fully constructed :class:`Element` objects.

The most powerful tool for doing this is :class:`XMLPullParser`.  It does not
require a blocking read to obtain the XML data, and is instead fed with data
incrementally with :meth:`XMLPullParser.feed` calls.  To get the parsed XML
elements, call :meth:`XMLPullParser.read_events`.  Here is an example::

   >>> parser = ET.XMLPullParser(['start', 'end'])
   >>> parser.feed('<mytag>sometext')
   >>> list(parser.read_events())
   [('start', <Element 'mytag' at 0x7fa66db2be58>)]
   >>> parser.feed(' more text</mytag>')
   >>> for event, elem in parser.read_events():
   ...     print(event)
   ...     print(elem.tag, 'text=', elem.text)
   ...
   end

The obvious use case is applications that operate in a non-blocking fashion
where the XML data is being received from a socket or read incrementally from
some storage device.  In such cases, blocking reads are unacceptable.

Because it's so flexible, :class:`XMLPullParser` can be inconvenient to use for
simpler use-cases.  If you don't mind your application blocking on reading XML
data but would still like to have incremental parsing capabilities, take a look
at :func:`iterparse`.  It can be useful when you're reading a large XML document
and don't want to hold it wholly in memory.

Finding interesting elements
^^^^^^^^^^^^^^^^^^^^^^^^^^^^

:class:`Element` has some useful methods that help iterate recursively over all
the sub-tree below it (its children, their children, and so on).  For example,
:meth:`Element.iter`::

   >>> for neighbor in root.iter('neighbor'):
   ...     print(neighbor.attrib)
   ...
   {'name': 'Austria', 'direction': 'E'}
   {'name': 'Switzerland', 'direction': 'W'}
   {'name': 'Malaysia', 'direction': 'N'}
   {'name': 'Costa Rica', 'direction': 'W'}
   {'name': 'Colombia', 'direction': 'E'}

:meth:`Element.findall` finds only elements with a tag which are direct
children of the current element.  :meth:`Element.find` finds the *first* child
with a particular tag, and :attr:`Element.text` accesses the element's text
content.  :meth:`Element.get` accesses the element's attributes::

   >>> for country in root.findall('country'):
   ...     rank = country.find('rank').text
   ...     name = country.get('name')
   ...     print(name, rank)
   ...
   Liechtenstein 1
   Singapore 4
   Panama 68

More sophisticated specification of which elements to look for is possible by
using :ref:`XPath <elementtree-xpath>`.

Modifying an XML File
^^^^^^^^^^^^^^^^^^^^^

:class:`ElementTree` provides a simple way to build XML documents and write them to files.
The :meth:`ElementTree.write` method serves this purpose.

Once created, an :class:`Element` object may be manipulated by directly changing
its fields (such as :attr:`Element.text`), adding and modifying attributes
(:meth:`Element.set` method), as well as adding new children (for example
with :meth:`Element.append`).

Let's say we want to add one to each country's rank, and add an ``updated``
attribute to the rank element::

   >>> for rank in root.iter('rank'):
   ...     new_rank = int(rank.text) + 1
   ...     rank.text = str(new_rank)
   ...     rank.set('updated', 'yes')
   ...
   >>> tree.write('output.xml')

Our XML now looks like this:

.. code-block:: xml

   <?xml version="1.0"?>
   <data>
       <country name="Liechtenstein">
           <rank updated="yes">2</rank>
           <year>2008</year>
           <gdppc>141100</gdppc>
           <neighbor name="Austria" direction="E"/>
           <neighbor name="Switzerland" direction="W"/>
       </country>
       <country name="Singapore">
           <rank updated="yes">5</rank>
           <year>2011</year>
           <gdppc>59900</gdppc>
           <neighbor name="Malaysia" direction="N"/>
       </country>
       <country name="Panama">
           <rank updated="yes">69</rank>
           <year>2011</year>
           <gdppc>13600</gdppc>
           <neighbor name="Costa Rica" direction="W"/>
           <neighbor name="Colombia" direction="E"/>
       </country>
   </data>

We can remove elements using :meth:`Element.remove`.  Let's say we want to
remove all countries with a rank higher than 50::

   >>> for country in root.findall('country'):
   ...     # using root.findall() to avoid removal during traversal
   ...     rank = int(country.find('rank').text)
   ...     if rank > 50:
   ...         root.remove(country)
   ...
   >>> tree.write('output.xml')

Note that concurrent modification while iterating can lead to problems,
just like when iterating and modifying Python lists or dicts.
Therefore, the example first collects all matching elements with
``root.findall()``, and only then iterates over the list of matches.

Our XML now looks like this:

.. code-block:: xml

   <?xml version="1.0"?>
   <data>
       <country name="Liechtenstein">
           <rank updated="yes">2</rank>
           <year>2008</year>
           <gdppc>141100</gdppc>
           <neighbor name="Austria" direction="E"/>
           <neighbor name="Switzerland" direction="W"/>
       </country>
       <country name="Singapore">
           <rank updated="yes">5</rank>
           <year>2011</year>
           <gdppc>59900</gdppc>
           <neighbor name="Malaysia" direction="N"/>
       </country>
   </data>

Building XML documents
^^^^^^^^^^^^^^^^^^^^^^

The :func:`SubElement` function also provides a convenient way to create new
sub-elements for a given element::

   >>> a = ET.Element('a')
   >>> b = ET.SubElement(a, 'b')
   >>> c = ET.SubElement(a, 'c')
   >>> d = ET.SubElement(c, 'd')
   >>> ET.dump(a)
   <a><b /><c><d /></c></a>

Parsing XML with Namespaces
^^^^^^^^^^^^^^^^^^^^^^^^^^^

If the XML input has `namespaces
<https://en.wikipedia.org/wiki/XML_namespace>`__, tags and attributes
with prefixes in the form ``prefix:sometag`` get expanded to
``{uri}sometag`` where the *prefix* is replaced by the full *URI*.
Also, if there is a `default namespace
<https://www.w3.org/TR/xml-names/#defaulting>`__,
that full URI gets prepended to all of the non-prefixed tags.

Here is an XML example that incorporates two namespaces, one with the
prefix "fictional" and the other serving as the default namespace:

.. code-block:: xml

    <?xml version="1.0"?>
    <actors xmlns:fictional="http://characters.example.com"
            xmlns="http://people.example.com">
        <actor>
            <name>John Cleese</name>
            <fictional:character>Lancelot</fictional:character>
            <fictional:character>Archie Leach</fictional:character>
        </actor>
        <actor>
            <name>Eric Idle</name>
            <fictional:character>Sir Robin</fictional:character>
            <fictional:character>Gunther</fictional:character>
            <fictional:character>Commander Clement</fictional:character>
        </actor>
    </actors>

One way to search and explore this XML example is to manually add the
URI to every tag or attribute in the xpath of a
:meth:`~Element.find` or :meth:`~Element.findall`::

    root = fromstring(xml_text)
    for actor in root.findall('{http://people.example.com}actor'):
        name = actor.find('{http://people.example.com}name')
        print(name.text)
        for char in actor.findall('{http://characters.example.com}character'):
            print(' |-->', char.text)

A better way to search the namespaced XML example is to create a
dictionary with your own prefixes and use those in the search functions::

    ns = {'real_person': 'http://people.example.com',
          'role': 'http://characters.example.com'}

    for actor in root.findall('real_person:actor', ns):
        name = actor.find('real_person:name', ns)
        print(name.text)
        for char in actor.findall('role:character', ns):
            print(' |-->', char.text)

These two approaches both output::

    John Cleese
     |--> Lancelot
     |--> Archie Leach
    Eric Idle
     |--> Sir Robin
     |--> Gunther
     |--> Commander Clement


.. _elementtree-xpath:

XPath support
-------------

This module provides limited support for
`XPath expressions <https://www.w3.org/TR/xpath>`_ for locating elements in a
tree.  The goal is to support a small subset of the abbreviated syntax; a full
XPath engine is outside the scope of the module.

Example
^^^^^^^

Here's an example that demonstrates some of the XPath capabilities of the
module.  We'll be using the ``countrydata`` XML document from the
:ref:`Parsing XML <elementtree-parsing-xml>` section::

   import xml.etree.ElementTree as ET

   root = ET.fromstring(countrydata)

   # Top-level elements
   root.findall(".")

   # All 'neighbor' grand-children of 'country' children of the top-level
   # elements
   root.findall("./country/neighbor")

   # Nodes with name='Singapore' that have a 'year' child
   root.findall(".//year/..[@name='Singapore']")

   # 'year' nodes that are children of nodes with name='Singapore'
   root.findall(".//*[@name='Singapore']/year")

   # All 'neighbor' nodes that are the second child of their parent
   root.findall(".//neighbor[2]")

For XML with namespaces, use the usual qualified ``{namespace}tag`` notation::

   # All dublin-core "title" tags in the document
   root.findall(".//{http://purl.org/dc/elements/1.1/}title")


Supported XPath syntax
^^^^^^^^^^^^^^^^^^^^^^

.. tabularcolumns:: |l|L|

+-----------------------+------------------------------------------------------+
| Syntax                | Meaning                                              |
+=======================+======================================================+
| ``tag``               | Selects all child elements with the given tag.       |
|                       | For example, ``spam`` selects all child elements     |
|                       | named ``spam``, and ``spam/egg`` selects all         |
|                       | grandchildren named ``egg`` in all children named    |
|                       | ``spam``.  ``{namespace}*`` selects all tags in the  |
|                       | given namespace, ``{*}spam`` selects tags named      |
|                       | ``spam`` in any (or no) namespace, and ``{}*``       |
|                       | only selects tags that are not in a namespace.       |
|                       |                                                      |
|                       | .. versionchanged:: 3.8                              |
|                       |    Support for star-wildcards was added.             |
+-----------------------+------------------------------------------------------+
| ``*``                 | Selects all child elements, including comments and   |
|                       | processing instructions.  For example, ``*/egg``     |
|                       | selects all grandchildren named ``egg``.             |
+-----------------------+------------------------------------------------------+
| ``.``                 | Selects the current node.  This is mostly useful     |
|                       | at the beginning of the path, to indicate that it's  |
|                       | a relative path.                                     |
+-----------------------+------------------------------------------------------+
| ``//``                | Selects all subelements, on all levels beneath the   |
|                       | current  element.  For example, ``.//egg`` selects   |
|                       | all ``egg`` elements in the entire tree.             |
+-----------------------+------------------------------------------------------+
| ``..``                | Selects the parent element.  Returns ``None`` if the |
|                       | path attempts to reach the ancestors of the start    |
|                       | element (the element ``find`` was called on).        |
+-----------------------+------------------------------------------------------+
| ``[@attrib]``         | Selects all elements that have the given attribute.  |
+-----------------------+------------------------------------------------------+
| ``[@attrib='value']`` | Selects all elements for which the given attribute   |
|                       | has the given value.  The value cannot contain       |
|                       | quotes.                                              |
+-----------------------+------------------------------------------------------+
| ``[@attrib!='value']``| Selects all elements for which the given attribute   |
|                       | does not have the given value. The value cannot      |
|                       | contain quotes.                                      |
|                       |                                                      |
|                       | .. versionadded:: 3.10                               |
+-----------------------+------------------------------------------------------+
| ``[tag]``             | Selects all elements that have a child named         |
|                       | ``tag``.  Only immediate children are supported.     |
+-----------------------+------------------------------------------------------+
| ``[.='text']``        | Selects all elements whose complete text content,    |
|                       | including descendants, equals the given ``text``.    |
|                       |                                                      |
|                       | .. versionadded:: 3.7                                |
+-----------------------+------------------------------------------------------+
| ``[.!='text']``       | Selects all elements whose complete text content,    |
|                       | including descendants, does not equal the given      |
|                       | ``text``.                                            |
|                       |                                                      |
|                       | .. versionadded:: 3.10                               |
+-----------------------+------------------------------------------------------+
| ``[tag='text']``      | Selects all elements that have a child named         |
|                       | ``tag`` whose complete text content, including       |
|                       | descendants, equals the given ``text``.              |
+-----------------------+------------------------------------------------------+
| ``[tag!='text']``     | Selects all elements that have a child named         |
|                       | ``tag`` whose complete text content, including       |
|                       | descendants, does not equal the given ``text``.      |
|                       |                                                      |
|                       | .. versionadded:: 3.10                               |
+-----------------------+------------------------------------------------------+
| ``[position]``        | Selects all elements that are located at the given   |
|                       | position.  The position can be either an integer     |
|                       | (1 is the first position), the expression ``last()`` |
|                       | (for the last position), or a position relative to   |
|                       | the last position (e.g. ``last()-1``).               |
+-----------------------+------------------------------------------------------+

Predicates (expressions within square brackets) must be preceded by a tag
name, an asterisk, or another predicate.  ``position`` predicates must be
preceded by a tag name.

Reference
---------

.. _elementtree-functions:

Functions
^^^^^^^^^

.. function:: canonicalize(xml_data=None, *, out=None, from_file=None, **options)

   `C14N 2.0 <https://www.w3.org/TR/xml-c14n2/>`_ transformation function.

   Canonicalization is a way to normalise XML output in a way that allows
   byte-by-byte comparisons and digital signatures.  It reduced the freedom
   that XML serializers have and instead generates a more constrained XML
   representation.  The main restrictions regard the placement of namespace
   declarations, the ordering of attributes, and ignorable whitespace.

   This function takes an XML data string (*xml_data*) or a file path or
   file-like object (*from_file*) as input, converts it to the canonical
   form, and writes it out using the *out* file(-like) object, if provided,
   or returns it as a text string if not.  The output file receives text,
   not bytes.  It should therefore be opened in text mode with ``utf-8``
   encoding.

   Typical uses::

      xml_data = "<root>...</root>"
      print(canonicalize(xml_data))

      with open("c14n_output.xml", mode='w', encoding='utf-8') as out_file:
          canonicalize(xml_data, out=out_file)

      with open("c14n_output.xml", mode='w', encoding='utf-8') as out_file:
          canonicalize(from_file="inputfile.xml", out=out_file)

   The configuration *options* are as follows:

   - *with_comments*: set to true to include comments (default: false)
   - *strip_text*: set to true to strip whitespace before and after text content
                   (default: false)
   - *rewrite_prefixes*: set to true to replace namespace prefixes by "n{number}"
                         (default: false)
   - *qname_aware_tags*: a set of qname aware tag names in which prefixes
                         should be replaced in text content (default: empty)
   - *qname_aware_attrs*: a set of qname aware attribute names in which prefixes
                          should be replaced in text content (default: empty)
   - *exclude_attrs*: a set of attribute names that should not be serialised
   - *exclude_tags*: a set of tag names that should not be serialised

   In the option list above, "a set" refers to any collection or iterable of
   strings, no ordering is expected.

   .. versionadded:: 3.8


.. function:: Comment(text=None)

   Comment element factory.  This factory function creates a special element
   that will be serialized as an XML comment by the standard serializer.  The
   comment string can be either a bytestring or a Unicode string.  *text* is a
   string containing the comment string.  Returns an element instance
   representing a comment.

   Note that :class:`XMLParser` skips over comments in the input
   instead of creating comment objects for them. An :class:`ElementTree` will
   only contain comment nodes if they have been inserted into to
   the tree using one of the :class:`Element` methods.

.. function:: dump(elem)

   Writes an element tree or element structure to sys.stdout.  This function
   should be used for debugging only.

   The exact output format is implementation dependent.  In this version, it's
   written as an ordinary XML file.

   *elem* is an element tree or an individual element.

   .. versionchanged:: 3.8
      The :func:`dump` function now preserves the attribute order specified
      by the user.


.. function:: fromstring(text, parser=None)

   Parses an XML section from a string constant.  Same as :func:`XML`.  *text*
   is a string containing XML data.  *parser* is an optional parser instance.
   If not given, the standard :class:`XMLParser` parser is used.
   Returns an :class:`Element` instance.


.. function:: fromstringlist(sequence, parser=None)

   Parses an XML document from a sequence of string fragments.  *sequence* is a
   list or other sequence containing XML data fragments.  *parser* is an
   optional parser instance.  If not given, the standard :class:`XMLParser`
   parser is used.  Returns an :class:`Element` instance.

   .. versionadded:: 3.2


.. function:: indent(tree, space="  ", level=0)

   Appends whitespace to the subtree to indent the tree visually.
   This can be used to generate pretty-printed XML output.
   *tree* can be an Element or ElementTree.  *space* is the whitespace
   string that will be inserted for each indentation level, two space
   characters by default.  For indenting partial subtrees inside of an
   already indented tree, pass the initial indentation level as *level*.

   .. versionadded:: 3.9


.. function:: iselement(element)

   Check if an object appears to be a valid element object.  *element* is an
   element instance.  Return ``True`` if this is an element object.


.. function:: iterparse(source, events=None, parser=None)

   Parses an XML section into an element tree incrementally, and reports what's
   going on to the user.  *source* is a filename or :term:`file object`
   containing XML data.  *events* is a sequence of events to report back.  The
   supported events are the strings ``"start"``, ``"end"``, ``"comment"``,
   ``"pi"``, ``"start-ns"`` and ``"end-ns"``
   (the "ns" events are used to get detailed namespace
   information).  If *events* is omitted, only ``"end"`` events are reported.
   *parser* is an optional parser instance.  If not given, the standard
   :class:`XMLParser` parser is used.  *parser* must be a subclass of
   :class:`XMLParser` and can only use the default :class:`TreeBuilder` as a
   target.  Returns an :term:`iterator` providing ``(event, elem)`` pairs.

   Note that while :func:`iterparse` builds the tree incrementally, it issues
   blocking reads on *source* (or the file it names).  As such, it's unsuitable
   for applications where blocking reads can't be made.  For fully non-blocking
   parsing, see :class:`XMLPullParser`.

   .. note::

      :func:`iterparse` only guarantees that it has seen the ">" character of a
      starting tag when it emits a "start" event, so the attributes are defined,
      but the contents of the text and tail attributes are undefined at that
      point.  The same applies to the element children; they may or may not be
      present.

      If you need a fully populated element, look for "end" events instead.

   .. deprecated:: 3.4
      The *parser* argument.

   .. versionchanged:: 3.8
      The ``comment`` and ``pi`` events were added.


.. function:: parse(source, parser=None)

   Parses an XML section into an element tree.  *source* is a filename or file
   object containing XML data.  *parser* is an optional parser instance.  If
   not given, the standard :class:`XMLParser` parser is used.  Returns an
   :class:`ElementTree` instance.


.. function:: ProcessingInstruction(target, text=None)

   PI element factory.  This factory function creates a special element that
   will be serialized as an XML processing instruction.  *target* is a string
   containing the PI target.  *text* is a string containing the PI contents, if
   given.  Returns an element instance, representing a processing instruction.

   Note that :class:`XMLParser` skips over processing instructions
   in the input instead of creating comment objects for them. An
   :class:`ElementTree` will only contain processing instruction nodes if
   they have been inserted into to the tree using one of the
   :class:`Element` methods.

.. function:: register_namespace(prefix, uri)

   Registers a namespace prefix.  The registry is global, and any existing
   mapping for either the given prefix or the namespace URI will be removed.
   *prefix* is a namespace prefix.  *uri* is a namespace uri.  Tags and
   attributes in this namespace will be serialized with the given prefix, if at
   all possible.

   .. versionadded:: 3.2


.. function:: SubElement(parent, tag, attrib={}, **extra)

   Subelement factory.  This function creates an element instance, and appends
   it to an existing element.

   The element name, attribute names, and attribute values can be either
   bytestrings or Unicode strings.  *parent* is the parent element.  *tag* is
   the subelement name.  *attrib* is an optional dictionary, containing element
   attributes.  *extra* contains additional attributes, given as keyword
   arguments.  Returns an element instance.


.. function:: tostring(element, encoding="us-ascii", method="xml", *, \
                       xml_declaration=None, default_namespace=None, \
                       short_empty_elements=True)

   Generates a string representation of an XML element, including all
   subelements.  *element* is an :class:`Element` instance.  *encoding* [1]_ is
   the output encoding (default is US-ASCII).  Use ``encoding="unicode"`` to
   generate a Unicode string (otherwise, a bytestring is generated).  *method*
   is either ``"xml"``, ``"html"`` or ``"text"`` (default is ``"xml"``).
   *xml_declaration*, *default_namespace* and *short_empty_elements* has the same
   meaning as in :meth:`ElementTree.write`. Returns an (optionally) encoded string
   containing the XML data.

   .. versionadded:: 3.4
      The *short_empty_elements* parameter.

   .. versionadded:: 3.8
      The *xml_declaration* and *default_namespace* parameters.

   .. versionchanged:: 3.8
      The :func:`tostring` function now preserves the attribute order
      specified by the user.


.. function:: tostringlist(element, encoding="us-ascii", method="xml", *, \
                           xml_declaration=None, default_namespace=None, \
                           short_empty_elements=True)

   Generates a string representation of an XML element, including all
   subelements.  *element* is an :class:`Element` instance.  *encoding* [1]_ is
   the output encoding (default is US-ASCII).  Use ``encoding="unicode"`` to
   generate a Unicode string (otherwise, a bytestring is generated).  *method*
   is either ``"xml"``, ``"html"`` or ``"text"`` (default is ``"xml"``).
   *xml_declaration*, *default_namespace* and *short_empty_elements* has the same
   meaning as in :meth:`ElementTree.write`. Returns a list of (optionally) encoded
   strings containing the XML data. It does not guarantee any specific sequence,
   except that ``b"".join(tostringlist(element)) == tostring(element)``.

   .. versionadded:: 3.2

   .. versionadded:: 3.4
      The *short_empty_elements* parameter.

   .. versionadded:: 3.8
      The *xml_declaration* and *default_namespace* parameters.

   .. versionchanged:: 3.8
      The :func:`tostringlist` function now preserves the attribute order
      specified by the user.


.. function:: XML(text, parser=None)

   Parses an XML section from a string constant.  This function can be used to
   embed "XML literals" in Python code.  *text* is a string containing XML
   data.  *parser* is an optional parser instance.  If not given, the standard
   :class:`XMLParser` parser is used.  Returns an :class:`Element` instance.


.. function:: XMLID(text, parser=None)

   Parses an XML section from a string constant, and also returns a dictionary
   which maps from element id:s to elements.  *text* is a string containing XML
   data.  *parser* is an optional parser instance.  If not given, the standard
   :class:`XMLParser` parser is used.  Returns a tuple containing an
   :class:`Element` instance and a dictionary.


.. _elementtree-xinclude:

XInclude support
----------------

This module provides limited support for
`XInclude directives <https://www.w3.org/TR/xinclude/>`_, via the :mod:`xml.etree.ElementInclude` helper module.  This module can be used to insert subtrees and text strings into element trees, based on information in the tree.

Example
^^^^^^^

Here's an example that demonstrates use of the XInclude module. To include an XML document in the current document, use the ``{http://www.w3.org/2001/XInclude}include`` element and set the **parse** attribute to ``"xml"``, and use the **href** attribute to specify the document to include.

.. code-block:: xml

    <?xml version="1.0"?>
    <document xmlns:xi="http://www.w3.org/2001/XInclude">
      <xi:include href="source.xml" parse="xml" />
    </document>

By default, the **href** attribute is treated as a file name. You can use custom loaders to override this behaviour. Also note that the standard helper does not support XPointer syntax.

To process this file, load it as usual, and pass the root element to the :mod:`xml.etree.ElementTree` module:

.. code-block:: python

   from xml.etree import ElementTree, ElementInclude

   tree = ElementTree.parse("document.xml")
   root = tree.getroot()

   ElementInclude.include(root)

The ElementInclude module replaces the ``{http://www.w3.org/2001/XInclude}include`` element with the root element from the **source.xml** document. The result might look something like this:

.. code-block:: xml

    <document xmlns:xi="http://www.w3.org/2001/XInclude">
      <para>This is a paragraph.</para>
    </document>

If the **parse** attribute is omitted, it defaults to "xml". The href attribute is required.

To include a text document, use the ``{http://www.w3.org/2001/XInclude}include`` element, and set the **parse** attribute to "text":

.. code-block:: xml

    <?xml version="1.0"?>
    <document xmlns:xi="http://www.w3.org/2001/XInclude">
      Copyright (c) <xi:include href="year.txt" parse="text" />.
    </document>

The result might look something like:

.. code-block:: xml

    <document xmlns:xi="http://www.w3.org/2001/XInclude">
      Copyright (c) 2003.
    </document>

Reference
---------

.. _elementinclude-functions:

Functions
^^^^^^^^^

.. function:: xml.etree.ElementInclude.default_loader( href, parse, encoding=None)

   Default loader. This default loader reads an included resource from disk.  *href* is a URL.
   *parse* is for parse mode either "xml" or "text".  *encoding*
   is an optional text encoding.  If not given, encoding is ``utf-8``.  Returns the
   expanded resource.  If the parse mode is ``"xml"``, this is an ElementTree
   instance.  If the parse mode is "text", this is a Unicode string.  If the
   loader fails, it can return None or raise an exception.


.. function:: xml.etree.ElementInclude.include( elem, loader=None, base_url=None, \
                                                max_depth=6)

   This function expands XInclude directives.  *elem* is the root element.  *loader* is
   an optional resource loader.  If omitted, it defaults to :func:`default_loader`.
   If given, it should be a callable that implements the same interface as
   :func:`default_loader`.  *base_url* is base URL of the original file, to resolve
   relative include file references.  *max_depth* is the maximum number of recursive
   inclusions.  Limited to reduce the risk of malicious content explosion. Pass a
   negative value to disable the limitation.

   Returns the expanded resource.  If the parse mode is
   ``"xml"``, this is an ElementTree instance.  If the parse mode is "text",
   this is a Unicode string.  If the loader fails, it can return None or
   raise an exception.

   .. versionadded:: 3.9
      The *base_url* and *max_depth* parameters.


.. _elementtree-element-objects:

Element Objects
^^^^^^^^^^^^^^^

.. class:: Element(tag, attrib={}, **extra)

   Element class.  This class defines the Element interface, and provides a
   reference implementation of this interface.

   The element name, attribute names, and attribute values can be either
   bytestrings or Unicode strings.  *tag* is the element name.  *attrib* is
   an optional dictionary, containing element attributes.  *extra* contains
   additional attributes, given as keyword arguments.


   .. attribute:: tag

      A string identifying what kind of data this element represents (the
      element type, in other words).


   .. attribute:: text
                  tail

      These attributes can be used to hold additional data associated with
      the element.  Their values are usually strings but may be any
      application-specific object.  If the element is created from
      an XML file, the *text* attribute holds either the text between
      the element's start tag and its first child or end tag, or ``None``, and
      the *tail* attribute holds either the text between the element's
      end tag and the next tag, or ``None``.  For the XML data

      .. code-block:: xml

         <a><b>1<c>2<d/>3</c></b>4</a>

      the *a* element has ``None`` for both *text* and *tail* attributes,
      the *b* element has *text* ``"1"`` and *tail* ``"4"``,
      the *c* element has *text* ``"2"`` and *tail* ``None``,
      and the *d* element has *text* ``None`` and *tail* ``"3"``.

      To collect the inner text of an element, see :meth:`itertext`, for
      example ``"".join(element.itertext())``.

      Applications may store arbitrary objects in these attributes.


   .. attribute:: attrib

      A dictionary containing the element's attributes.  Note that while the
      *attrib* value is always a real mutable Python dictionary, an ElementTree
      implementation may choose to use another internal representation, and
      create the dictionary only if someone asks for it.  To take advantage of
      such implementations, use the dictionary methods below whenever possible.

   The following dictionary-like methods work on the element attributes.


   .. method:: clear()

      Resets an element.  This function removes all subelements, clears all
      attributes, and sets the text and tail attributes to ``None``.


   .. method:: get(key, default=None)

      Gets the element attribute named *key*.

      Returns the attribute value, or *default* if the attribute was not found.


   .. method:: items()

      Returns the element attributes as a sequence of (name, value) pairs.  The
      attributes are returned in an arbitrary order.


   .. method:: keys()

      Returns the elements attribute names as a list.  The names are returned
      in an arbitrary order.


   .. method:: set(key, value)

      Set the attribute *key* on the element to *value*.

   The following methods work on the element's children (subelements).


   .. method:: append(subelement)

      Adds the element *subelement* to the end of this element's internal list
      of subelements.  Raises :exc:`TypeError` if *subelement* is not an
      :class:`Element`.


   .. method:: extend(subelements)

      Appends *subelements* from a sequence object with zero or more elements.
      Raises :exc:`TypeError` if a subelement is not an :class:`Element`.

      .. versionadded:: 3.2


   .. method:: find(match, namespaces=None)

      Finds the first subelement matching *match*.  *match* may be a tag name
      or a :ref:`path <elementtree-xpath>`.  Returns an element instance
      or ``None``.  *namespaces* is an optional mapping from namespace prefix
      to full name.  Pass ``''`` as prefix to move all unprefixed tag names
      in the expression into the given namespace.


   .. method:: findall(match, namespaces=None)

      Finds all matching subelements, by tag name or
      :ref:`path <elementtree-xpath>`.  Returns a list containing all matching
      elements in document order.  *namespaces* is an optional mapping from
      namespace prefix to full name.  Pass ``''`` as prefix to move all
      unprefixed tag names in the expression into the given namespace.


   .. method:: findtext(match, default=None, namespaces=None)

      Finds text for the first subelement matching *match*.  *match* may be
      a tag name or a :ref:`path <elementtree-xpath>`.  Returns the text content
      of the first matching element, or *default* if no element was found.
      Note that if the matching element has no text content an empty string
      is returned. *namespaces* is an optional mapping from namespace prefix
      to full name.  Pass ``''`` as prefix to move all unprefixed tag names
      in the expression into the given namespace.


   .. method:: insert(index, subelement)

      Inserts *subelement* at the given position in this element.  Raises
      :exc:`TypeError` if *subelement* is not an :class:`Element`.


   .. method:: iter(tag=None)

      Creates a tree :term:`iterator` with the current element as the root.
      The iterator iterates over this element and all elements below it, in
      document (depth first) order.  If *tag* is not ``None`` or ``'*'``, only
      elements whose tag equals *tag* are returned from the iterator.  If the
      tree structure is modified during iteration, the result is undefined.

      .. versionadded:: 3.2


   .. method:: iterfind(match, namespaces=None)

      Finds all matching subelements, by tag name or
      :ref:`path <elementtree-xpath>`.  Returns an iterable yielding all
      matching elements in document order. *namespaces* is an optional mapping
      from namespace prefix to full name.


      .. versionadded:: 3.2


   .. method:: itertext()

      Creates a text iterator.  The iterator loops over this element and all
      subelements, in document order, and returns all inner text.

      .. versionadded:: 3.2


   .. method:: makeelement(tag, attrib)

      Creates a new element object of the same type as this element.  Do not
      call this method, use the :func:`SubElement` factory function instead.


   .. method:: remove(subelement)

      Removes *subelement* from the element.  Unlike the find\* methods this
      method compares elements based on the instance identity, not on tag value
      or contents.

   :class:`Element` objects also support the following sequence type methods
   for working with subelements: :meth:`~object.__delitem__`,
   :meth:`~object.__getitem__`, :meth:`~object.__setitem__`,
   :meth:`~object.__len__`.

   Caution: Elements with no subelements will test as ``False``.  This behavior
   will change in future versions.  Use specific ``len(elem)`` or ``elem is
   None`` test instead. ::

     element = root.find('foo')

     if not element:  # careful!
         print("element not found, or element has no subelements")

     if element is None:
         print("element not found")

   Prior to Python 3.8, the serialisation order of the XML attributes of
   elements was artificially made predictable by sorting the attributes by
   their name. Based on the now guaranteed ordering of dicts, this arbitrary
   reordering was removed in Python 3.8 to preserve the order in which
   attributes were originally parsed or created by user code.

   In general, user code should try not to depend on a specific ordering of
   attributes, given that the `XML Information Set
   <https://www.w3.org/TR/xml-infoset/>`_ explicitly excludes the attribute
   order from conveying information. Code should be prepared to deal with
   any ordering on input. In cases where deterministic XML output is required,
   e.g. for cryptographic signing or test data sets, canonical serialisation
   is available with the :func:`canonicalize` function.

   In cases where canonical output is not applicable but a specific attribute
   order is still desirable on output, code should aim for creating the
   attributes directly in the desired order, to avoid perceptual mismatches
   for readers of the code. In cases where this is difficult to achieve, a
   recipe like the following can be applied prior to serialisation to enforce
   an order independently from the Element creation::

     def reorder_attributes(root):
         for el in root.iter():
             attrib = el.attrib
             if len(attrib) > 1:
                 # adjust attribute order, e.g. by sorting
                 attribs = sorted(attrib.items())
                 attrib.clear()
                 attrib.update(attribs)


.. _elementtree-elementtree-objects:

ElementTree Objects
^^^^^^^^^^^^^^^^^^^


.. class:: ElementTree(element=None, file=None)

   ElementTree wrapper class.  This class represents an entire element
   hierarchy, and adds some extra support for serialization to and from
   standard XML.

   *element* is the root element.  The tree is initialized with the contents
   of the XML *file* if given.


   .. method:: _setroot(element)

      Replaces the root element for this tree.  This discards the current
      contents of the tree, and replaces it with the given element.  Use with
      care.  *element* is an element instance.


   .. method:: find(match, namespaces=None)

      Same as :meth:`Element.find`, starting at the root of the tree.


   .. method:: findall(match, namespaces=None)

      Same as :meth:`Element.findall`, starting at the root of the tree.


   .. method:: findtext(match, default=None, namespaces=None)

      Same as :meth:`Element.findtext`, starting at the root of the tree.


   .. method:: getroot()

      Returns the root element for this tree.


   .. method:: iter(tag=None)

      Creates and returns a tree iterator for the root element.  The iterator
      loops over all elements in this tree, in section order.  *tag* is the tag
      to look for (default is to return all elements).


   .. method:: iterfind(match, namespaces=None)

      Same as :meth:`Element.iterfind`, starting at the root of the tree.

      .. versionadded:: 3.2


   .. method:: parse(source, parser=None)

      Loads an external XML section into this element tree.  *source* is a file
      name or :term:`file object`.  *parser* is an optional parser instance.
      If not given, the standard :class:`XMLParser` parser is used.  Returns the
      section root element.


   .. method:: write(file, encoding="us-ascii", xml_declaration=None, \
                     default_namespace=None, method="xml", *, \
                     short_empty_elements=True)

      Writes the element tree to a file, as XML.  *file* is a file name, or a
      :term:`file object` opened for writing.  *encoding* [1]_ is the output
      encoding (default is US-ASCII).
      *xml_declaration* controls if an XML declaration should be added to the
      file.  Use ``False`` for never, ``True`` for always, ``None``
      for only if not US-ASCII or UTF-8 or Unicode (default is ``None``).
      *default_namespace* sets the default XML namespace (for "xmlns").
      *method* is either ``"xml"``, ``"html"`` or ``"text"`` (default is
      ``"xml"``).
      The keyword-only *short_empty_elements* parameter controls the formatting
      of elements that contain no content.  If ``True`` (the default), they are
      emitted as a single self-closed tag, otherwise they are emitted as a pair
      of start/end tags.

      The output is either a string (:class:`str`) or binary (:class:`bytes`).
      This is controlled by the *encoding* argument.  If *encoding* is
      ``"unicode"``, the output is a string; otherwise, it's binary.  Note that
      this may conflict with the type of *file* if it's an open
      :term:`file object`; make sure you do not try to write a string to a
      binary stream and vice versa.

      .. versionadded:: 3.4
         The *short_empty_elements* parameter.

      .. versionchanged:: 3.8
         The :meth:`write` method now preserves the attribute order specified
         by the user.


This is the XML file that is going to be manipulated::

    <html>
        <head>
            <title>Example page</title>
        </head>
        <body>
            <p>Moved to <a href="http://example.org/">example.org</a>
            or <a href="http://example.com/">example.com</a>.</p>
        </body>
    </html>

Example of changing the attribute "target" of every link in first paragraph::

    >>> from xml.etree.ElementTree import ElementTree
    >>> tree = ElementTree()
    >>> tree.parse("index.xhtml")
    <Element 'html' at 0xb77e6fac>
    >>> p = tree.find("body/p")     # Finds first occurrence of tag p in body
    >>> p
    <Element 'p' at 0xb77ec26c>
    >>> links = list(p.iter("a"))   # Returns list of all links
    >>> links
    [<Element 'a' at 0xb77ec2ac>, <Element 'a' at 0xb77ec1cc>]
    >>> for i in links:             # Iterates through all found links
    ...     i.attrib["target"] = "blank"
    >>> tree.write("output.xhtml")

.. _elementtree-qname-objects:

QName Objects
^^^^^^^^^^^^^


.. class:: QName(text_or_uri, tag=None)

   QName wrapper.  This can be used to wrap a QName attribute value, in order
   to get proper namespace handling on output.  *text_or_uri* is a string
   containing the QName value, in the form {uri}local, or, if the tag argument
   is given, the URI part of a QName.  If *tag* is given, the first argument is
   interpreted as a URI, and this argument is interpreted as a local name.
   :class:`QName` instances are opaque.



.. _elementtree-treebuilder-objects:

TreeBuilder Objects
^^^^^^^^^^^^^^^^^^^


.. class:: TreeBuilder(element_factory=None, *, comment_factory=None, \
                       pi_factory=None, insert_comments=False, insert_pis=False)

   Generic element structure builder.  This builder converts a sequence of
   start, data, end, comment and pi method calls to a well-formed element
   structure.  You can use this class to build an element structure using
   a custom XML parser, or a parser for some other XML-like format.

   *element_factory*, when given, must be a callable accepting two positional
   arguments: a tag and a dict of attributes.  It is expected to return a new
   element instance.

   The *comment_factory* and *pi_factory* functions, when given, should behave
   like the :func:`Comment` and :func:`ProcessingInstruction` functions to
   create comments and processing instructions.  When not given, the default
   factories will be used.  When *insert_comments* and/or *insert_pis* is true,
   comments/pis will be inserted into the tree if they appear within the root
   element (but not outside of it).

   .. method:: close()

      Flushes the builder buffers, and returns the toplevel document
      element.  Returns an :class:`Element` instance.


   .. method:: data(data)

      Adds text to the current element.  *data* is a string.  This should be
      either a bytestring, or a Unicode string.


   .. method:: end(tag)

      Closes the current element.  *tag* is the element name.  Returns the
      closed element.


   .. method:: start(tag, attrs)

      Opens a new element.  *tag* is the element name.  *attrs* is a dictionary
      containing element attributes.  Returns the opened element.


   .. method:: comment(text)

      Creates a comment with the given *text*.  If ``insert_comments`` is true,
      this will also add it to the tree.

      .. versionadded:: 3.8


   .. method:: pi(target, text)

      Creates a comment with the given *target* name and *text*.  If
      ``insert_pis`` is true, this will also add it to the tree.

      .. versionadded:: 3.8


   In addition, a custom :class:`TreeBuilder` object can provide the
   following methods:

   .. method:: doctype(name, pubid, system)

      Handles a doctype declaration.  *name* is the doctype name.  *pubid* is
      the public identifier.  *system* is the system identifier.  This method
      does not exist on the default :class:`TreeBuilder` class.

      .. versionadded:: 3.2

   .. method:: start_ns(prefix, uri)

      Is called whenever the parser encounters a new namespace declaration,
      before the ``start()`` callback for the opening element that defines it.
      *prefix* is ``''`` for the default namespace and the declared
      namespace prefix name otherwise.  *uri* is the namespace URI.

      .. versionadded:: 3.8

   .. method:: end_ns(prefix)

      Is called after the ``end()`` callback of an element that declared
      a namespace prefix mapping, with the name of the *prefix* that went
      out of scope.

      .. versionadded:: 3.8


.. class:: C14NWriterTarget(write, *, \
             with_comments=False, strip_text=False, rewrite_prefixes=False, \
             qname_aware_tags=None, qname_aware_attrs=None, \
             exclude_attrs=None, exclude_tags=None)

   A `C14N 2.0 <https://www.w3.org/TR/xml-c14n2/>`_ writer.  Arguments are the
   same as for the :func:`canonicalize` function.  This class does not build a
   tree but translates the callback events directly into a serialised form
   using the *write* function.

   .. versionadded:: 3.8


.. _elementtree-xmlparser-objects:

XMLParser Objects
^^^^^^^^^^^^^^^^^


.. class:: XMLParser(*, target=None, encoding=None)

   This class is the low-level building block of the module.  It uses
   :mod:`xml.parsers.expat` for efficient, event-based parsing of XML.  It can
   be fed XML data incrementally with the :meth:`feed` method, and parsing
   events are translated to a push API - by invoking callbacks on the *target*
   object.  If *target* is omitted, the standard :class:`TreeBuilder` is used.
   If *encoding* [1]_ is given, the value overrides the
   encoding specified in the XML file.

   .. versionchanged:: 3.8
      Parameters are now :ref:`keyword-only <keyword-only_parameter>`.
      The *html* argument no longer supported.


   .. method:: close()

      Finishes feeding data to the parser.  Returns the result of calling the
      ``close()`` method of the *target* passed during construction; by default,
      this is the toplevel document element.


   .. method:: feed(data)

      Feeds data to the parser.  *data* is encoded data.

   :meth:`XMLParser.feed` calls *target*\'s ``start(tag, attrs_dict)`` method
   for each opening tag, its ``end(tag)`` method for each closing tag, and data
   is processed by method ``data(data)``.  For further supported callback
   methods, see the :class:`TreeBuilder` class.  :meth:`XMLParser.close` calls
   *target*\'s method ``close()``. :class:`XMLParser` can be used not only for
   building a tree structure. This is an example of counting the maximum depth
   of an XML file::

    >>> from xml.etree.ElementTree import XMLParser
    >>> class MaxDepth:                     # The target object of the parser
    ...     maxDepth = 0
    ...     depth = 0
    ...     def start(self, tag, attrib):   # Called for each opening tag.
    ...         self.depth += 1
    ...         if self.depth > self.maxDepth:
    ...             self.maxDepth = self.depth
    ...     def end(self, tag):             # Called for each closing tag.
    ...         self.depth -= 1
    ...     def data(self, data):
    ...         pass            # We do not need to do anything with data.
    ...     def close(self):    # Called when all data has been parsed.
    ...         return self.maxDepth
    ...
    >>> target = MaxDepth()
    >>> parser = XMLParser(target=target)
    >>> exampleXml = """
    ... <a>
    ...   <b>
    ...   </b>
    ...   <b>
    ...     <c>
    ...       <d>
    ...       </d>
    ...     </c>
    ...   </b>
    ... </a>"""
    >>> parser.feed(exampleXml)
    >>> parser.close()
    4


.. _elementtree-xmlpullparser-objects:

XMLPullParser Objects
^^^^^^^^^^^^^^^^^^^^^

.. class:: XMLPullParser(events=None)

   A pull parser suitable for non-blocking applications.  Its input-side API is
   similar to that of :class:`XMLParser`, but instead of pushing calls to a
   callback target, :class:`XMLPullParser` collects an internal list of parsing
   events and lets the user read from it. *events* is a sequence of events to
   report back.  The supported events are the strings ``"start"``, ``"end"``,
   ``"comment"``, ``"pi"``, ``"start-ns"`` and ``"end-ns"`` (the "ns" events
   are used to get detailed namespace information).  If *events* is omitted,
   only ``"end"`` events are reported.

   .. method:: feed(data)

      Feed the given bytes data to the parser.

   .. method:: close()

      Signal the parser that the data stream is terminated. Unlike
      :meth:`XMLParser.close`, this method always returns :const:`None`.
      Any events not yet retrieved when the parser is closed can still be
      read with :meth:`read_events`.

   .. method:: read_events()

      Return an iterator over the events which have been encountered in the
      data fed to the
      parser.  The iterator yields ``(event, elem)`` pairs, where *event* is a
      string representing the type of event (e.g. ``"end"``) and *elem* is the
      encountered :class:`Element` object, or other context value as follows.

      * ``start``, ``end``: the current Element.
      * ``comment``, ``pi``: the current comment / processing instruction
      * ``start-ns``: a tuple ``(prefix, uri)`` naming the declared namespace
        mapping.
      * ``end-ns``: :const:`None` (this may change in a future version)

      Events provided in a previous call to :meth:`read_events` will not be
      yielded again.  Events are consumed from the internal queue only when
      they are retrieved from the iterator, so multiple readers iterating in
      parallel over iterators obtained from :meth:`read_events` will have
      unpredictable results.

   .. note::

      :class:`XMLPullParser` only guarantees that it has seen the ">"
      character of a starting tag when it emits a "start" event, so the
      attributes are defined, but the contents of the text and tail attributes
      are undefined at that point.  The same applies to the element children;
      they may or may not be present.

      If you need a fully populated element, look for "end" events instead.

   .. versionadded:: 3.4

   .. versionchanged:: 3.8
      The ``comment`` and ``pi`` events were added.


Exceptions
^^^^^^^^^^

.. class:: ParseError

   XML parse error, raised by the various parsing methods in this module when
   parsing fails.  The string representation of an instance of this exception
   will contain a user-friendly error message.  In addition, it will have
   the following attributes available:

   .. attribute:: code

      A numeric error code from the expat parser. See the documentation of
      :mod:`xml.parsers.expat` for the list of error codes and their meanings.

   .. attribute:: position

      A tuple of *line*, *column* numbers, specifying where the error occurred.

.. rubric:: Footnotes

.. [1] The encoding string included in XML output should conform to the
   appropriate standards.  For example, "UTF-8" is valid, but "UTF8" is
   not.  See https://www.w3.org/TR/2006/REC-xml11-20060816/#NT-EncodingDecl
   and https://www.iana.org/assignments/character-sets/character-sets.xhtml.