How to use the soupsieve.css_types.SelectorList function in soupsieve

def _freeze_relations(self, relations):
        """Freeze relation."""

        if relations:
            sel = relations[0]
            sel.relations.extend(relations[1:])
            return ct.SelectorList([sel.freeze()])
        else:
            return ct.SelectorList()

sel.nth.append(ct.SelectorNth(1, False, 0, False, True, ct.SelectorList()))
            elif pseudo == ':first-of-type':
                sel.nth.append(ct.SelectorNth(1, False, 0, True, False, ct.SelectorList()))
            elif pseudo == ':last-of-type':
                sel.nth.append(ct.SelectorNth(1, False, 0, True, True, ct.SelectorList()))
            elif pseudo == ':only-child':
                sel.nth.extend(
                    [
                        ct.SelectorNth(1, False, 0, False, False, ct.SelectorList()),
                        ct.SelectorNth(1, False, 0, False, True, ct.SelectorList())
                    ]
                )
            elif pseudo == ':only-of-type':
                sel.nth.extend(
                    [
                        ct.SelectorNth(1, False, 0, True, False, ct.SelectorList()),
                        ct.SelectorNth(1, False, 0, True, True, ct.SelectorList())
                    ]
                )
            has_selector = True
        elif complex_pseudo and pseudo in PSEUDO_COMPLEX_NO_MATCH:
            self.parse_selectors(iselector, m.end(0), FLG_PSEUDO | FLG_OPEN)
            sel.no_match = True
            has_selector = True
        elif not complex_pseudo and pseudo in PSEUDO_SIMPLE_NO_MATCH:
            sel.no_match = True
            has_selector = True
        elif pseudo in PSEUDO_SUPPORTED:
            raise SelectorSyntaxError(
                "Invalid syntax for pseudo class '{}'".format(pseudo),
                self.pattern,
                m.start(0)

elif pseudo == ":required":
                sel.selectors.append(CSS_REQUIRED)
            elif pseudo == ":optional":
                sel.selectors.append(CSS_OPTIONAL)
            elif pseudo == ":read-only":
                sel.selectors.append(CSS_READ_ONLY)
            elif pseudo == ":read-write":
                sel.selectors.append(CSS_READ_WRITE)
            elif pseudo == ":in-range":
                sel.selectors.append(CSS_IN_RANGE)
            elif pseudo == ":out-of-range":
                sel.selectors.append(CSS_OUT_OF_RANGE)
            elif pseudo == ":placeholder-shown":
                sel.selectors.append(CSS_PLACEHOLDER_SHOWN)
            elif pseudo == ':first-child':
                sel.nth.append(ct.SelectorNth(1, False, 0, False, False, ct.SelectorList()))
            elif pseudo == ':last-child':
                sel.nth.append(ct.SelectorNth(1, False, 0, False, True, ct.SelectorList()))
            elif pseudo == ':first-of-type':
                sel.nth.append(ct.SelectorNth(1, False, 0, True, False, ct.SelectorList()))
            elif pseudo == ':last-of-type':
                sel.nth.append(ct.SelectorNth(1, False, 0, True, True, ct.SelectorList()))
            elif pseudo == ':only-child':
                sel.nth.extend(
                    [
                        ct.SelectorNth(1, False, 0, False, False, ct.SelectorList()),
                        ct.SelectorNth(1, False, 0, False, True, ct.SelectorList())
                    ]
                )
            elif pseudo == ':only-of-type':
                sel.nth.extend(
                    [

# Some patterns require additional logic, such as default. We try to make these the
        # last pattern, and append the appropriate flag to that selector which communicates
        # to the matcher what additional logic is required.
        if is_default:
            selectors[-1].flags = ct.SEL_DEFAULT
        if is_indeterminate:
            selectors[-1].flags = ct.SEL_INDETERMINATE
        if is_in_range:
            selectors[-1].flags = ct.SEL_IN_RANGE
        if is_out_of_range:
            selectors[-1].flags = ct.SEL_OUT_OF_RANGE
        if is_placeholder_shown:
            selectors[-1].flags = ct.SEL_PLACEHOLDER_SHOWN

        return ct.SelectorList([s.freeze() for s in selectors], is_not, is_html)

Parse custom pseudo class alias.

        Compile custom selectors as we need them. When compiling a custom selector,
        set it to `None` in the dictionary so we can avoid an infinite loop.
        """

        pseudo = util.lower(css_unescape(m.group('name')))
        selector = self.custom.get(pseudo)
        if selector is None:
            raise SelectorSyntaxError(
                "Undefined custom selector '{}' found at postion {}".format(pseudo, m.end(0)),
                self.pattern,
                m.end(0)
            )

        if not isinstance(selector, ct.SelectorList):
            self.custom[pseudo] = None
            selector = CSSParser(
                selector, custom=self.custom, flags=self.flags
            ).process_selectors(flags=FLG_PSEUDO)
            self.custom[pseudo] = selector

        sel.selectors.append(selector)
        has_selector = True
        return has_selector

else:
            # Value matches
            pattern = re.compile(r'^%s$' % re.escape(value), flags)
            if op.startswith('!'):
                # Equivalent to `:not([attr=value])`
                inverse = True
        if is_type and pattern:
            pattern2 = re.compile(pattern.pattern)

        # Append the attribute selector
        sel_attr = ct.SelectorAttribute(attr, ns, pattern, pattern2)
        if inverse:
            # If we are using `!=`, we need to nest the pattern under a `:not()`.
            sub_sel = _Selector()
            sub_sel.attributes.append(sel_attr)
            not_list = ct.SelectorList([sub_sel.freeze()], True, False)
            sel.selectors.append(not_list)
        else:
            sel.attributes.append(sel_attr)

        has_selector = True
        return has_selector