:mod:`urllib.parse` --- Parse URLs into components
==================================================

.. module:: urllib.parse
   :synopsis: Parse URLs into or assemble them from components.

**Source code:** :source:`Lib/urllib/parse.py`

.. index::
   single: WWW
   single: World Wide Web
   single: URL
   pair: URL; parsing
   pair: relative; URL

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

This module defines a standard interface to break Uniform Resource Locator (URL)
strings up in components (addressing scheme, network location, path etc.), to
combine the components back into a URL string, and to convert a "relative URL"
to an absolute URL given a "base URL."

The module has been designed to match the Internet RFC on Relative Uniform
Resource Locators. It supports the following URL schemes: ``file``, ``ftp``,
``gopher``, ``hdl``, ``http``, ``https``, ``imap``, ``mailto``, ``mms``,
``news``, ``nntp``, ``prospero``, ``rsync``, ``rtsp``, ``rtspu``, ``sftp``,
``shttp``, ``sip``, ``sips``, ``snews``, ``svn``, ``svn+ssh``, ``telnet``,
``wais``, ``ws``, ``wss``.

The :mod:`urllib.parse` module defines functions that fall into two broad
categories: URL parsing and URL quoting. These are covered in detail in
the following sections.

URL Parsing
-----------

The URL parsing functions focus on splitting a URL string into its components,
or on combining URL components into a URL string.

.. function:: urlparse(urlstring, scheme='', allow_fragments=True)

   Parse a URL into six components, returning a 6-tuple.  This corresponds to the
   general structure of a URL: ``scheme://netloc/path;parameters?query#fragment``.
   Each tuple item is a string, possibly empty. The components are not broken up in
   smaller parts (for example, the network location is a single string), and %
   escapes are not expanded. The delimiters as shown above are not part of the
   result, except for a leading slash in the *path* component, which is retained if
   present.  For example:

      >>> from urllib.parse import urlparse
      >>> o = urlparse('http://www.cwi.nl:80/%7Eguido/Python.html')
      >>> o   # doctest: +NORMALIZE_WHITESPACE
      ParseResult(scheme='http', netloc='www.cwi.nl:80', path='/%7Eguido/Python.html',
                  params='', query='', fragment='')
      >>> o.scheme
      'http'
      >>> o.port
      80
      >>> o.geturl()
      'http://www.cwi.nl:80/%7Eguido/Python.html'

   Following the syntax specifications in :rfc:`1808`, urlparse recognizes
   a netloc only if it is properly introduced by '//'.  Otherwise the
   input is presumed to be a relative URL and thus to start with
   a path component.

   .. doctest::
      :options: +NORMALIZE_WHITESPACE

       >>> from urllib.parse import urlparse
       >>> urlparse('//www.cwi.nl:80/%7Eguido/Python.html')
       ParseResult(scheme='', netloc='www.cwi.nl:80', path='/%7Eguido/Python.html',
                  params='', query='', fragment='')
       >>> urlparse('www.cwi.nl/%7Eguido/Python.html')
       ParseResult(scheme='', netloc='', path='www.cwi.nl/%7Eguido/Python.html',
                  params='', query='', fragment='')
       >>> urlparse('help/Python.html')
       ParseResult(scheme='', netloc='', path='help/Python.html', params='',
                  query='', fragment='')

   The *scheme* argument gives the default addressing scheme, to be
   used only if the URL does not specify one.  It should be the same type
   (text or bytes) as *urlstring*, except that the default value ``''`` is
   always allowed, and is automatically converted to ``b''`` if appropriate.

   If the *allow_fragments* argument is false, fragment identifiers are not
   recognized.  Instead, they are parsed as part of the path, parameters
   or query component, and :attr:`fragment` is set to the empty string in
   the return value.

   The return value is actually an instance of a subclass of :class:`tuple`.  This
   class has the following additional read-only convenience attributes:

   +------------------+-------+--------------------------+----------------------+
   | Attribute        | Index | Value                    | Value if not present |
   +==================+=======+==========================+======================+
   | :attr:`scheme`   | 0     | URL scheme specifier     | *scheme* parameter   |
   +------------------+-------+--------------------------+----------------------+
   | :attr:`netloc`   | 1     | Network location part    | empty string         |
   +------------------+-------+--------------------------+----------------------+
   | :attr:`path`     | 2     | Hierarchical path        | empty string         |
   +------------------+-------+--------------------------+----------------------+
   | :attr:`params`   | 3     | Parameters for last path | empty string         |
   |                  |       | element                  |                      |
   +------------------+-------+--------------------------+----------------------+
   | :attr:`query`    | 4     | Query component          | empty string         |
   +------------------+-------+--------------------------+----------------------+
   | :attr:`fragment` | 5     | Fragment identifier      | empty string         |
   +------------------+-------+--------------------------+----------------------+
   | :attr:`username` |       | User name                | :const:`None`        |
   +------------------+-------+--------------------------+----------------------+
   | :attr:`password` |       | Password                 | :const:`None`        |
   +------------------+-------+--------------------------+----------------------+
   | :attr:`hostname` |       | Host name (lower case)   | :const:`None`        |
   +------------------+-------+--------------------------+----------------------+
   | :attr:`port`     |       | Port number as integer,  | :const:`None`        |
   |                  |       | if present               |                      |
   +------------------+-------+--------------------------+----------------------+

   Reading the :attr:`port` attribute will raise a :exc:`ValueError` if
   an invalid port is specified in the URL.  See section
   :ref:`urlparse-result-object` for more information on the result object.

   Unmatched square brackets in the :attr:`netloc` attribute will raise a
   :exc:`ValueError`.

   Characters in the :attr:`netloc` attribute that decompose under NFKC
   normalization (as used by the IDNA encoding) into any of ``/``, ``?``,
   ``#``, ``@``, or ``:`` will raise a :exc:`ValueError`. If the URL is
   decomposed before parsing, no error will be raised.

   .. versionchanged:: 3.2
      Added IPv6 URL parsing capabilities.

   .. versionchanged:: 3.3
      The fragment is now parsed for all URL schemes (unless *allow_fragment* is
      false), in accordance with :rfc:`3986`.  Previously, a whitelist of
      schemes that support fragments existed.

   .. versionchanged:: 3.6
      Out-of-range port numbers now raise :exc:`ValueError`, instead of
      returning :const:`None`.

   .. versionchanged:: 3.7.3
      Characters that affect netloc parsing under NFKC normalization will
      now raise :exc:`ValueError`.


.. function:: parse_qs(qs, keep_blank_values=False, strict_parsing=False, encoding='utf-8', errors='replace', max_num_fields=None)

   Parse a query string given as a string argument (data of type
   :mimetype:`application/x-www-form-urlencoded`).  Data are returned as a
   dictionary.  The dictionary keys are the unique query variable names and the
   values are lists of values for each name.

   The optional argument *keep_blank_values* is a flag indicating whether blank
   values in percent-encoded queries should be treated as blank strings. A true value
   indicates that blanks should be retained as  blank strings.  The default false
   value indicates that blank values are to be ignored and treated as if they were
   not included.

   The optional argument *strict_parsing* is a flag indicating what to do with
   parsing errors.  If false (the default), errors are silently ignored.  If true,
   errors raise a :exc:`ValueError` exception.

   The optional *encoding* and *errors* parameters specify how to decode
   percent-encoded sequences into Unicode characters, as accepted by the
   :meth:`bytes.decode` method.

   The optional argument *max_num_fields* is the maximum number of fields to
   read. If set, then throws a :exc:`ValueError` if there are more than
   *max_num_fields* fields read.

   Use the :func:`urllib.parse.urlencode` function (with the ``doseq``
   parameter set to ``True``) to convert such dictionaries into query
   strings.

   .. versionchanged:: 3.2
      Add *encoding* and *errors* parameters.

   .. versionchanged:: 3.7.2
      Added *max_num_fields* parameter.


.. function:: parse_qsl(qs, keep_blank_values=False, strict_parsing=False, encoding='utf-8', errors='replace', max_num_fields=None)

   Parse a query string given as a string argument (data of type
   :mimetype:`application/x-www-form-urlencoded`).  Data are returned as a list of
   name, value pairs.

   The optional argument *keep_blank_values* is a flag indicating whether blank
   values in percent-encoded queries should be treated as blank strings. A true value
   indicates that blanks should be retained as  blank strings.  The default false
   value indicates that blank values are to be ignored and treated as if they were
   not included.

   The optional argument *strict_parsing* is a flag indicating what to do with
   parsing errors.  If false (the default), errors are silently ignored.  If true,
   errors raise a :exc:`ValueError` exception.

   The optional *encoding* and *errors* parameters specify how to decode
   percent-encoded sequences into Unicode characters, as accepted by the
   :meth:`bytes.decode` method.

   The optional argument *max_num_fields* is the maximum number of fields to
   read. If set, then throws a :exc:`ValueError` if there are more than
   *max_num_fields* fields read.

   Use the :func:`urllib.parse.urlencode` function to convert such lists of pairs into
   query strings.

   .. versionchanged:: 3.2
      Add *encoding* and *errors* parameters.

   .. versionchanged:: 3.7.2
      Added *max_num_fields* parameter.

.. function:: urlunparse(parts)

   Construct a URL from a tuple as returned by ``urlparse()``. The *parts*
   argument can be any six-item iterable. This may result in a slightly
   different, but equivalent URL, if the URL that was parsed originally had
   unnecessary delimiters (for example, a ``?`` with an empty query; the RFC
   states that these are equivalent).


.. function:: urlsplit(urlstring, scheme='', allow_fragments=True)

   This is similar to :func:`urlparse`, but does not split the params from the URL.
   This should generally be used instead of :func:`urlparse` if the more recent URL
   syntax allowing parameters to be applied to each segment of the *path* portion
   of the URL (see :rfc:`2396`) is wanted.  A separate function is needed to
   separate the path segments and parameters.  This function returns a 5-tuple:
   (addressing scheme, network location, path, query, fragment identifier).

   The return value is actually an instance of a subclass of :class:`tuple`.  This
   class has the following additional read-only convenience attributes:

   +------------------+-------+-------------------------+----------------------+
   | Attribute        | Index | Value                   | Value if not present |
   +==================+=======+=========================+======================+
   | :attr:`scheme`   | 0     | URL scheme specifier    | *scheme* parameter   |
   +------------------+-------+-------------------------+----------------------+
   | :attr:`netloc`   | 1     | Network location part   | empty string         |
   +------------------+-------+-------------------------+----------------------+
   | :attr:`path`     | 2     | Hierarchical path       | empty string         |
   +------------------+-------+-------------------------+----------------------+
   | :attr:`query`    | 3     | Query component         | empty string         |
   +------------------+-------+-------------------------+----------------------+
   | :attr:`fragment` | 4     | Fragment identifier     | empty string         |
   +------------------+-------+-------------------------+----------------------+
   | :attr:`username` |       | User name               | :const:`None`        |
   +------------------+-------+-------------------------+----------------------+
   | :attr:`password` |       | Password                | :const:`None`        |
   +------------------+-------+-------------------------+----------------------+
   | :attr:`hostname` |       | Host name (lower case)  | :const:`None`        |
   +------------------+-------+-------------------------+----------------------+
   | :attr:`port`     |       | Port number as integer, | :const:`None`        |
   |                  |       | if present              |                      |
   +------------------+-------+-------------------------+----------------------+

   Reading the :attr:`port` attribute will raise a :exc:`ValueError` if
   an invalid port is specified in the URL.  See section
   :ref:`urlparse-result-object` for more information on the result object.

   Unmatched square brackets in the :attr:`netloc` attribute will raise a
   :exc:`ValueError`.

   Characters in the :attr:`netloc` attribute that decompose under NFKC
   normalization (as used by the IDNA encoding) into any of ``/``, ``?``,
   ``#``, ``@``, or ``:`` will raise a :exc:`ValueError`. If the URL is
   decomposed before parsing, no error will be raised.

   .. versionchanged:: 3.6
      Out-of-range port numbers now raise :exc:`ValueError`, instead of
      returning :const:`None`.

   .. versionchanged:: 3.7.3
      Characters that affect netloc parsing under NFKC normalization will
      now raise :exc:`ValueError`.


.. function:: urlunsplit(parts)

   Combine the elements of a tuple as returned by :func:`urlsplit` into a
   complete URL as a string. The *parts* argument can be any five-item
   iterable. This may result in a slightly different, but equivalent URL, if the
   URL that was parsed originally had unnecessary delimiters (for example, a ?
   with an empty query; the RFC states that these are equivalent).


.. function:: urljoin(base, url, allow_fragments=True)

   Construct a full ("absolute") URL by combining a "base URL" (*base*) with
   another URL (*url*).  Informally, this uses components of the base URL, in
   particular the addressing scheme, the network location and (part of) the
   path, to provide missing components in the relative URL.  For example:

      >>> from urllib.parse import urljoin
      >>> urljoin('http://www.cwi.nl/%7Eguido/Python.html', 'FAQ.html')
      'http://www.cwi.nl/%7Eguido/FAQ.html'

   The *allow_fragments* argument has the same meaning and default as for
   :func:`urlparse`.

   .. note::

      If *url* is an absolute URL (that is, starting with ``//`` or ``scheme://``),
      the *url*'s host name and/or scheme will be present in the result.  For example:

   .. doctest::

      >>> urljoin('http://www.cwi.nl/%7Eguido/Python.html',
      ...         '//www.python.org/%7Eguido')
      'http://www.python.org/%7Eguido'

   If you do not want that behavior, preprocess the *url* with :func:`urlsplit` and
   :func:`urlunsplit`, removing possible *scheme* and *netloc* parts.


   .. versionchanged:: 3.5

      Behaviour updated to match the semantics defined in :rfc:`3986`.


.. function:: urldefrag(url)

   If *url* contains a fragment identifier, return a modified version of *url*
   with no fragment identifier, and the fragment identifier as a separate
   string.  If there is no fragment identifier in *url*, return *url* unmodified
   and an empty string.

   The return value is actually an instance of a subclass of :class:`tuple`.  This
   class has the following additional read-only convenience attributes:

   +------------------+-------+-------------------------+----------------------+
   | Attribute        | Index | Value                   | Value if not present |
   +==================+=======+=========================+======================+
   | :attr:`url`      | 0     | URL with no fragment    | empty string         |
   +------------------+-------+-------------------------+----------------------+
   | :attr:`fragment` | 1     | Fragment identifier     | empty string         |
   +------------------+-------+-------------------------+----------------------+

   See section :ref:`urlparse-result-object` for more information on the result
   object.

   .. versionchanged:: 3.2
      Result is a structured object rather than a simple 2-tuple.

.. _parsing-ascii-encoded-bytes:

Parsing ASCII Encoded Bytes
---------------------------

The URL parsing functions were originally designed to operate on character
strings only. In practice, it is useful to be able to manipulate properly
quoted and encoded URLs as sequences of ASCII bytes. Accordingly, the
URL parsing functions in this module all operate on :class:`bytes` and
:class:`bytearray` objects in addition to :class:`str` objects.

If :class:`str` data is passed in, the result will also contain only
:class:`str` data. If :class:`bytes` or :class:`bytearray` data is
passed in, the result will contain only :class:`bytes` data.

Attempting to mix :class:`str` data with :class:`bytes` or
:class:`bytearray` in a single function call will result in a
:exc:`TypeError` being raised, while attempting to pass in non-ASCII
byte values will trigger :exc:`UnicodeDecodeError`.

To support easier conversion of result objects between :class:`str` and
:class:`bytes`, all return values from URL parsing functions provide
either an :meth:`encode` method (when the result contains :class:`str`
data) or a :meth:`decode` method (when the result contains :class:`bytes`
data). The signatures of these methods match those of the corresponding
:class:`str` and :class:`bytes` methods (except that the default encoding
is ``'ascii'`` rather than ``'utf-8'``). Each produces a value of a
corresponding type that contains either :class:`bytes` data (for
:meth:`encode` methods) or :class:`str` data (for
:meth:`decode` methods).

Applications that need to operate on potentially improperly quoted URLs
that may contain non-ASCII data will need to do their own decoding from
bytes to characters before invoking the URL parsing methods.

The behaviour described in this section applies only to the URL parsing
functions. The URL quoting functions use their own rules when producing
or consuming byte sequences as detailed in the documentation of the
individual URL quoting functions.

.. versionchanged:: 3.2
   URL parsing functions now accept ASCII encoded byte sequences


.. _urlparse-result-object:

Structured Parse Results
------------------------

The result objects from the :func:`urlparse`, :func:`urlsplit`  and
:func:`urldefrag` functions are subclasses of the :class:`tuple` type.
These subclasses add the attributes listed in the documentation for
those functions, the encoding and decoding support described in the
previous section, as well as an additional method:

.. method:: urllib.parse.SplitResult.geturl()

   Return the re-combined version of the original URL as a string. This may
   differ from the original URL in that the scheme may be normalized to lower
   case and empty components may be dropped. Specifically, empty parameters,
   queries, and fragment identifiers will be removed.

   For :func:`urldefrag` results, only empty fragment identifiers will be removed.
   For :func:`urlsplit` and :func:`urlparse` results, all noted changes will be
   made to the URL returned by this method.

   The result of this method remains unchanged if passed back through the original
   parsing function:

      >>> from urllib.parse import urlsplit
      >>> url = 'HTTP://www.Python.org/doc/#'
      >>> r1 = urlsplit(url)
      >>> r1.geturl()
      'http://www.Python.org/doc/'
      >>> r2 = urlsplit(r1.geturl())
      >>> r2.geturl()
      'http://www.Python.org/doc/'


The following classes provide the implementations of the structured parse
results when operating on :class:`str` objects:

.. class:: DefragResult(url, fragment)

   Concrete class for :func:`urldefrag` results containing :class:`str`
   data. The :meth:`encode` method returns a :class:`DefragResultBytes`
   instance.

   .. versionadded:: 3.2

.. class:: ParseResult(scheme, netloc, path, params, query, fragment)

   Concrete class for :func:`urlparse` results containing :class:`str`
   data. The :meth:`encode` method returns a :class:`ParseResultBytes`
   instance.

.. class:: SplitResult(scheme, netloc, path, query, fragment)

   Concrete class for :func:`urlsplit` results containing :class:`str`
   data. The :meth:`encode` method returns a :class:`SplitResultBytes`
   instance.


The following classes provide the implementations of the parse results when
operating on :class:`bytes` or :class:`bytearray` objects:

.. class:: DefragResultBytes(url, fragment)

   Concrete class for :func:`urldefrag` results containing :class:`bytes`
   data. The :meth:`decode` method returns a :class:`DefragResult`
   instance.

   .. versionadded:: 3.2

.. class:: ParseResultBytes(scheme, netloc, path, params, query, fragment)

   Concrete class for :func:`urlparse` results containing :class:`bytes`
   data. The :meth:`decode` method returns a :class:`ParseResult`
   instance.

   .. versionadded:: 3.2

.. class:: SplitResultBytes(scheme, netloc, path, query, fragment)

   Concrete class for :func:`urlsplit` results containing :class:`bytes`
   data. The :meth:`decode` method returns a :class:`SplitResult`
   instance.

   .. versionadded:: 3.2


URL Quoting
-----------

The URL quoting functions focus on taking program data and making it safe
for use as URL components by quoting special characters and appropriately
encoding non-ASCII text. They also support reversing these operations to
recreate the original data from the contents of a URL component if that
task isn't already covered by the URL parsing functions above.

.. function:: quote(string, safe='/', encoding=None, errors=None)

   Replace special characters in *string* using the ``%xx`` escape. Letters,
   digits, and the characters ``'_.-~'`` are never quoted. By default, this
   function is intended for quoting the path section of URL. The optional *safe*
   parameter specifies additional ASCII characters that should not be quoted
   --- its default value is ``'/'``.

   *string* may be either a :class:`str` or a :class:`bytes`.

   .. versionchanged:: 3.7
      Moved from :rfc:`2396` to :rfc:`3986` for quoting URL strings. "~" is now
      included in the set of reserved characters.

   The optional *encoding* and *errors* parameters specify how to deal with
   non-ASCII characters, as accepted by the :meth:`str.encode` method.
   *encoding* defaults to ``'utf-8'``.
   *errors* defaults to ``'strict'``, meaning unsupported characters raise a
   :class:`UnicodeEncodeError`.
   *encoding* and *errors* must not be supplied if *string* is a
   :class:`bytes`, or a :class:`TypeError` is raised.

   Note that ``quote(string, safe, encoding, errors)`` is equivalent to
   ``quote_from_bytes(string.encode(encoding, errors), safe)``.

   Example: ``quote('/El Niño/')`` yields ``'/El%20Ni%C3%B1o/'``.


.. function:: quote_plus(string, safe='', encoding=None, errors=None)

   Like :func:`quote`, but also replace spaces by plus signs, as required for
   quoting HTML form values when building up a query string to go into a URL.
   Plus signs in the original string are escaped unless they are included in
   *safe*.  It also does not have *safe* default to ``'/'``.

   Example: ``quote_plus('/El Niño/')`` yields ``'%2FEl+Ni%C3%B1o%2F'``.


.. function:: quote_from_bytes(bytes, safe='/')

   Like :func:`quote`, but accepts a :class:`bytes` object rather than a
   :class:`str`, and does not perform string-to-bytes encoding.

   Example: ``quote_from_bytes(b'a&\xef')`` yields
   ``'a%26%EF'``.


.. function:: unquote(string, encoding='utf-8', errors='replace')

   Replace ``%xx`` escapes by their single-character equivalent.
   The optional *encoding* and *errors* parameters specify how to decode
   percent-encoded sequences into Unicode characters, as accepted by the
   :meth:`bytes.decode` method.

   *string* must be a :class:`str`.

   *encoding* defaults to ``'utf-8'``.
   *errors* defaults to ``'replace'``, meaning invalid sequences are replaced
   by a placeholder character.

   Example: ``unquote('/El%20Ni%C3%B1o/')`` yields ``'/El Niño/'``.


.. function:: unquote_plus(string, encoding='utf-8', errors='replace')

   Like :func:`unquote`, but also replace plus signs by spaces, as required for
   unquoting HTML form values.

   *string* must be a :class:`str`.

   Example: ``unquote_plus('/El+Ni%C3%B1o/')`` yields ``'/El Niño/'``.


.. function:: unquote_to_bytes(string)

   Replace ``%xx`` escapes by their single-octet equivalent, and return a
   :class:`bytes` object.

   *string* may be either a :class:`str` or a :class:`bytes`.

   If it is a :class:`str`, unescaped non-ASCII characters in *string*
   are encoded into UTF-8 bytes.

   Example: ``unquote_to_bytes('a%26%EF')`` yields ``b'a&\xef'``.


.. function:: urlencode(query, doseq=False, safe='', encoding=None, \
                        errors=None, quote_via=quote_plus)

   Convert a mapping object or a sequence of two-element tuples, which may
   contain :class:`str` or :class:`bytes` objects, to a percent-encoded ASCII
   text string.  If the resultant string is to be used as a *data* for POST
   operation with the :func:`~urllib.request.urlopen` function, then
   it should be encoded to bytes, otherwise it would result in a
   :exc:`TypeError`.

   The resulting string is a series of ``key=value`` pairs separated by ``'&'``
   characters, where both *key* and *value* are quoted using the *quote_via*
   function.  By default, :func:`quote_plus` is used to quote the values, which
   means spaces are quoted as a ``'+'`` character and '/' characters are
   encoded as ``%2F``, which follows the standard for GET requests
   (``application/x-www-form-urlencoded``).  An alternate function that can be
   passed as *quote_via* is :func:`quote`, which will encode spaces as ``%20``
   and not encode '/' characters.  For maximum control of what is quoted, use
   ``quote`` and specify a value for *safe*.

   When a sequence of two-element tuples is used as the *query*
   argument, the first element of each tuple is a key and the second is a
   value. The value element in itself can be a sequence and in that case, if
   the optional parameter *doseq* is evaluates to ``True``, individual
   ``key=value`` pairs separated by ``'&'`` are generated for each element of
   the value sequence for the key.  The order of parameters in the encoded
   string will match the order of parameter tuples in the sequence.

   The *safe*, *encoding*, and *errors* parameters are passed down to
   *quote_via* (the *encoding* and *errors* parameters are only passed
   when a query element is a :class:`str`).

   To reverse this encoding process, :func:`parse_qs` and :func:`parse_qsl` are
   provided in this module to parse query strings into Python data structures.

   Refer to :ref:`urllib examples <urllib-examples>` to find out how urlencode
   method can be used for generating query string for a URL or data for POST.

   .. versionchanged:: 3.2
      Query parameter supports bytes and string objects.

   .. versionadded:: 3.5
      *quote_via* parameter.


.. seealso::

   :rfc:`3986` - Uniform Resource Identifiers
      This is the current standard (STD66). Any changes to urllib.parse module
      should conform to this. Certain deviations could be observed, which are
      mostly for backward compatibility purposes and for certain de-facto
      parsing requirements as commonly observed in major browsers.

   :rfc:`2732` - Format for Literal IPv6 Addresses in URL's.
      This specifies the parsing requirements of IPv6 URLs.

   :rfc:`2396` - Uniform Resource Identifiers (URI): Generic Syntax
      Document describing the generic syntactic requirements for both Uniform Resource
      Names (URNs) and Uniform Resource Locators (URLs).

   :rfc:`2368` - The mailto URL scheme.
      Parsing requirements for mailto URL schemes.

   :rfc:`1808` - Relative Uniform Resource Locators
      This Request For Comments includes the rules for joining an absolute and a
      relative URL, including a fair number of "Abnormal Examples" which govern the
      treatment of border cases.

   :rfc:`1738` - Uniform Resource Locators (URL)
      This specifies the formal syntax and semantics of absolute URLs.