Create an SGML/XML attribute string based on the items in a dict.
    All values that are neither `none` nor `undefined` are automatically
    escaped:

    .. sourcecode:: html+jinja

        <ul{{ {'class': 'my_list', 'missing': none,
                'id': 'list-%d'|format(variable)}|xmlattr }}>
        ...
        </ul>

    Results in something like this:

    .. sourcecode:: html

        <ul class="my_list" id="list-42">
        ...
        </ul>

    As you can see it automatically prepends a space in front of the item
    if the filter returned something unless the second parameter is false.

def do_xmlattr(_eval_ctx, d, autospace=True):
    """Create an SGML/XML attribute string based on the items in a dict.
    All values that are neither `none` nor `undefined` are automatically
    escaped:

    .. sourcecode:: html+jinja

        <ul{{ {'class': 'my_list', 'missing': none,
                'id': 'list-%d'|format(variable)}|xmlattr }}>
        ...
        </ul>

    Results in something like this:

    .. sourcecode:: html

        <ul class="my_list" id="list-42">
        ...
        </ul>

    As you can see it automatically prepends a space in front of the item
    if the filter returned something unless the second parameter is false.
    """
    rv = u' '.join(
        u'%s="%s"' % (escape(key), escape(value))
        for key, value in d.iteritems()
        if value is not None and not isinstance(value, Undefined)
    )
    if autospace and rv:
        rv = u' ' + rv
    if _eval_ctx.autoescape:
        rv = Markup(rv)
    return rv