How to use the soupsieve.util.lower function in soupsieve

def parse_pseudo_nth(self, sel, m, has_selector, iselector):
        """Parse `nth` pseudo."""

        mdict = m.groupdict()
        if mdict.get('pseudo_nth_child'):
            postfix = '_child'
        else:
            postfix = '_type'
        mdict['name'] = util.lower(css_unescape(mdict['name']))
        content = util.lower(mdict.get('nth' + postfix))
        if content == 'even':
            # 2n
            s1 = 2
            s2 = 0
            var = True
        elif content == 'odd':
            # 2n+1
            s1 = 2
            s2 = 1
            var = True
        else:
            nth_parts = RE_NTH.match(content)
            s1 = '-' if nth_parts.group('s1') and nth_parts.group('s1') == '-' else ''
            a = nth_parts.group('a')
            var = a.endswith('n')

def parse_attribute_selector(self, sel, m, has_selector):
        """Create attribute selector from the returned regex match."""

        inverse = False
        op = m.group('cmp')
        case = util.lower(m.group('case')) if m.group('case') else None
        ns = css_unescape(m.group('attr_ns')[:-1]) if m.group('attr_ns') else ''
        attr = css_unescape(m.group('attr_name'))
        is_type = False
        pattern2 = None

        if case:
            flags = re.I if case == 'i' else 0
        elif util.lower(attr) == 'type':
            flags = re.I
            is_type = True
        else:
            flags = 0

        if op:
            if m.group('value').startswith(('"', "'")):
                value = css_unescape(m.group('value')[1:-1], True)
            else:
                value = css_unescape(m.group('value'))
        else:
            value = None
        if not op:
            # Attribute name
            pattern = None
        elif op.startswith('^'):

root = self.root
        has_html_namespace = self.has_html_namespace

        # Walk parents looking for `lang` (HTML) or `xml:lang` XML property.
        parent = el
        found_lang = None
        last = None
        while not found_lang:
            has_html_ns = self.has_html_ns(parent)
            for k, v in self.iter_attributes(parent):
                attr_ns, attr = self.split_namespace(parent, k)
                if (
                    ((not has_ns or has_html_ns) and (util.lower(k) if not self.is_xml else k) == 'lang') or
                    (
                        has_ns and not has_html_ns and attr_ns == NS_XML and
                        (util.lower(attr) if not self.is_xml and attr is not None else attr) == 'lang'
                    )
                ):
                    found_lang = v
                    break
            last = parent
            parent = self.get_parent(parent, no_iframe=self.is_html)

            if parent is None:
                root = last
                has_html_namespace = self.has_html_ns(root)
                parent = last
                break

        # Use cached meta language.
        if not found_lang and self.cached_meta_lang:
            for cache in self.cached_meta_lang:

def is_iframe(self, el):
        """Check if element is an `iframe`."""

        return ((el.name if self.is_xml_tree(el) else util.lower(el.name)) == 'iframe') and self.is_html_tag(el)

def get_tag(self, el):
        """Get tag."""

        name = self.get_tag_name(el)
        return util.lower(name) if name is not None and not self.is_xml else name

def match_dir(self, el, directionality):
        """Check directionality."""

        # If we have to match both left and right, we can't match either.
        if directionality & ct.SEL_DIR_LTR and directionality & ct.SEL_DIR_RTL:
            return False

        if el is None or not self.is_html_tag(el):
            return False

        # Element has defined direction of left to right or right to left
        direction = DIR_MAP.get(util.lower(self.get_attribute_by_name(el, 'dir', '')), None)
        if direction not in (None, 0):
            return direction == directionality

        # Element is the document element (the root) and no direction assigned, assume left to right.
        is_root = self.is_root(el)
        if is_root and direction is None:
            return ct.SEL_DIR_LTR == directionality

        # If `input[type=telephone]` and no direction is assigned, assume left to right.
        name = self.get_tag(el)
        is_input = name == 'input'
        is_textarea = name == 'textarea'
        is_bdi = name == 'bdi'
        itype = util.lower(self.get_attribute_by_name(el, 'type', '')) if is_input else ''
        if is_input and itype == 'tel' and direction is None:
            return ct.SEL_DIR_LTR == directionality

# Element has defined direction of left to right or right to left
        direction = DIR_MAP.get(util.lower(self.get_attribute_by_name(el, 'dir', '')), None)
        if direction not in (None, 0):
            return direction == directionality

        # Element is the document element (the root) and no direction assigned, assume left to right.
        is_root = self.is_root(el)
        if is_root and direction is None:
            return ct.SEL_DIR_LTR == directionality

        # If `input[type=telephone]` and no direction is assigned, assume left to right.
        name = self.get_tag(el)
        is_input = name == 'input'
        is_textarea = name == 'textarea'
        is_bdi = name == 'bdi'
        itype = util.lower(self.get_attribute_by_name(el, 'type', '')) if is_input else ''
        if is_input and itype == 'tel' and direction is None:
            return ct.SEL_DIR_LTR == directionality

        # Auto handling for text inputs
        if ((is_input and itype in ('text', 'search', 'tel', 'url', 'email')) or is_textarea) and direction == 0:
            if is_textarea:
                value = []
                for node in self.get_contents(el, no_iframe=True):
                    if self.is_content_string(node):
                        value.append(node)
                value = ''.join(value)
            else:
                value = self.get_attribute_by_name(el, 'value', '')
            if value:
                for c in value:
                    bidi = unicodedata.bidirectional(c)

if f is form:
                found_form = True
                if t is el:
                    match = True
                break

        # We didn't have the form cached, so look for its default button
        if not found_form:
            for child in self.get_descendants(form, no_iframe=True):
                name = self.get_tag(child)
                # Can't do nested forms (haven't figured out why we never hit this)
                if name == 'form':  # pragma: no cover
                    break
                if name in ('input', 'button'):
                    v = self.get_attribute_by_name(child, 'type', '')
                    if v and util.lower(v) == 'submit':
                        self.cached_default_forms.append([form, child])
                        if el is child:
                            match = True
                        break
        return match

def is_break_tag(self, el):
        """Check if tag is an element we should break on."""

        name = sv.util.lower(el.name) if self.type != 'xhtml' else el.name
        return name in self.break_tags or name in self.user_break_tags

def process_custom(custom):
    """Process custom."""

    custom_selectors = {}
    if custom is not None:
        for key, value in custom.items():
            name = util.lower(key)
            if RE_CUSTOM.match(name) is None:
                raise SelectorSyntaxError("The name '{}' is not a valid custom pseudo-class name".format(name))
            if name in custom_selectors:
                raise KeyError("The custom selector '{}' has already been registered".format(name))
            custom_selectors[css_unescape(name)] = value
    return custom_selectors