mwparserfromhell/mwparserfromhell/parser/tokenizer.py

#
# Copyright (C) 2012-2020 Ben Kurtovic <ben.kurtovic@gmail.com>
#
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
# SOFTWARE.

import html.entities as htmlentities
from math import log
import re

from . import contexts, tokens
from .errors import ParserError
from ..definitions import (get_html_tag, is_parsable, is_single,
                           is_single_only, is_scheme)

__all__ = ["Tokenizer"]

class BadRoute(Exception):
    """Raised internally when the current tokenization route is invalid."""

    def __init__(self, context=0):
        super().__init__()
        self.context = context


class _TagOpenData:
    """Stores data about an HTML open tag, like ``<ref name="foo">``."""
    CX_NAME =        1 << 0
    CX_ATTR_READY =  1 << 1
    CX_ATTR_NAME =   1 << 2
    CX_ATTR_VALUE =  1 << 3
    CX_QUOTED =      1 << 4
    CX_NOTE_SPACE =  1 << 5
    CX_NOTE_EQUALS = 1 << 6
    CX_NOTE_QUOTE =  1 << 7

    def __init__(self):
        self.context = self.CX_NAME
        self.padding_buffer = {"first": "", "before_eq": "", "after_eq": ""}
        self.quoter = None
        self.reset = 0


class Tokenizer:
    """Creates a list of tokens from a string of wikicode."""
    USES_C = False
    START = object()
    END = object()
    MARKERS = ["{", "}", "[", "]", "<", ">", "|", "=", "&", "'", "#", "*", ";",
               ":", "/", "-", "!", "\n", START, END]
    MAX_DEPTH = 40
    regex = re.compile(r"([{}\[\]<>|=&'#*;:/\\\"\-!\n])", flags=re.IGNORECASE)
    tag_splitter = re.compile(r"([\s\"\'\\]+)")

    def __init__(self):
        self._text = None
        self._head = 0
        self._stacks = []
        self._global = 0
        self._depth = 0
        self._bad_routes = set()
        self._skip_style_tags = False

    @property
    def _stack(self):
        """The current token stack."""
        return self._stacks[-1][0]

    @property
    def _context(self):
        """The current token context."""
        return self._stacks[-1][1]

    @_context.setter
    def _context(self, value):
        self._stacks[-1][1] = value

    @property
    def _textbuffer(self):
        """The current textbuffer."""
        return self._stacks[-1][2]

    @_textbuffer.setter
    def _textbuffer(self, value):
        self._stacks[-1][2] = value

    @property
    def _stack_ident(self):
        """An identifier for the current stack.

        This is based on the starting head position and context. Stacks with
        the same identifier are always parsed in the same way. This can be used
        to cache intermediate parsing info.
        """
        return self._stacks[-1][3]

    def _push(self, context=0):
        """Add a new token stack, context, and textbuffer to the list."""
        new_ident = (self._head, context)
        if new_ident in self._bad_routes:
            raise BadRoute(context)

        self._stacks.append([[], context, [], new_ident])
        self._depth += 1

    def _push_textbuffer(self):
        """Push the textbuffer onto the stack as a Text node and clear it."""
        if self._textbuffer:
            self._stack.append(tokens.Text(text="".join(self._textbuffer)))
            self._textbuffer = []

    def _pop(self, keep_context=False):
        """Pop the current stack/context/textbuffer, returning the stack.

        If *keep_context* is ``True``, then we will replace the underlying
        stack's context with the current stack's.
        """
        self._push_textbuffer()
        self._depth -= 1
        if keep_context:
            context = self._context
            stack = self._stacks.pop()[0]
            self._context = context
            return stack
        return self._stacks.pop()[0]

    def _can_recurse(self):
        """Return whether or not our max recursion depth has been exceeded."""
        return self._depth < self.MAX_DEPTH

    def _memoize_bad_route(self):
        """Remember that the current route (head + context at push) is invalid.

        This will be noticed when calling _push with the same head and context,
        and the route will be failed immediately.
        """
        self._bad_routes.add(self._stack_ident)

    def _fail_route(self):
        """Fail the current tokenization route.

        Discards the current stack/context/textbuffer and raises
        :exc:`.BadRoute`.
        """
        context = self._context
        self._memoize_bad_route()
        self._pop()
        raise BadRoute(context)

    def _emit(self, token):
        """Write a token to the end of the current token stack."""
        self._push_textbuffer()
        self._stack.append(token)

    def _emit_first(self, token):
        """Write a token to the beginning of the current token stack."""
        self._push_textbuffer()
        self._stack.insert(0, token)

    def _emit_text(self, text):
        """Write text to the current textbuffer."""
        self._textbuffer.append(text)

    def _emit_all(self, tokenlist):
        """Write a series of tokens to the current stack at once."""
        if tokenlist and isinstance(tokenlist[0], tokens.Text):
            self._emit_text(tokenlist.pop(0).text)
        self._push_textbuffer()
        self._stack.extend(tokenlist)

    def _emit_text_then_stack(self, text):
        """Pop the current stack, write *text*, and then write the stack."""
        stack = self._pop()
        self._emit_text(text)
        if stack:
            self._emit_all(stack)
        self._head -= 1

    def _read(self, delta=0, wrap=False, strict=False):
        """Read the value at a relative point in the wikicode.

        The value is read from :attr:`self._head <_head>` plus the value of
        *delta* (which can be negative). If *wrap* is ``False``, we will not
        allow attempts to read from the end of the string if ``self._head +
        delta`` is negative. If *strict* is ``True``, the route will be failed
        (with :meth:`_fail_route`) if we try to read from past the end of the
        string; otherwise, :attr:`self.END <END>` is returned. If we try to
        read from before the start of the string, :attr:`self.START <START>` is
        returned.
        """
        index = self._head + delta
        if index < 0 and (not wrap or abs(index) > len(self._text)):
            return self.START
        try:
            return self._text[index]
        except IndexError:
            if strict:
                self._fail_route()
            return self.END

    def _parse_template(self, has_content):
        """Parse a template at the head of the wikicode string."""
        reset = self._head
        context = contexts.TEMPLATE_NAME
        if has_content:
            context |= contexts.HAS_TEMPLATE
        try:
            template = self._parse(context)
        except BadRoute:
            self._head = reset
            raise
        self._emit_first(tokens.TemplateOpen())
        self._emit_all(template)
        self._emit(tokens.TemplateClose())

    def _parse_argument(self):
        """Parse an argument at the head of the wikicode string."""
        reset = self._head
        try:
            argument = self._parse(contexts.ARGUMENT_NAME)
        except BadRoute:
            self._head = reset
            raise
        self._emit_first(tokens.ArgumentOpen())
        self._emit_all(argument)
        self._emit(tokens.ArgumentClose())

    def _parse_template_or_argument(self):
        """Parse a template or argument at the head of the wikicode string."""
        self._head += 2
        braces = 2
        while self._read() == "{":
            self._head += 1
            braces += 1
        has_content = False
        self._push()

        while braces:
            if braces == 1:
                return self._emit_text_then_stack("{")
            if braces == 2:
                try:
                    self._parse_template(has_content)
                except BadRoute:
                    return self._emit_text_then_stack("{{")
                break
            try:
                self._parse_argument()
                braces -= 3
            except BadRoute:
                try:
                    self._parse_template(has_content)
                    braces -= 2
                except BadRoute:
                    return self._emit_text_then_stack("{" * braces)
            if braces:
                has_content = True
                self._head += 1

        self._emit_all(self._pop())
        if self._context & contexts.FAIL_NEXT:
            self._context ^= contexts.FAIL_NEXT

    def _handle_template_param(self):
        """Handle a template parameter at the head of the string."""
        if self._context & contexts.TEMPLATE_NAME:
            if not self._context & (contexts.HAS_TEXT | contexts.HAS_TEMPLATE):
                self._fail_route()
            self._context ^= contexts.TEMPLATE_NAME
        elif self._context & contexts.TEMPLATE_PARAM_VALUE:
            self._context ^= contexts.TEMPLATE_PARAM_VALUE
        else:
            self._emit_all(self._pop())
        self._context |= contexts.TEMPLATE_PARAM_KEY
        self._emit(tokens.TemplateParamSeparator())
        self._push(self._context)

    def _handle_template_param_value(self):
        """Handle a template parameter's value at the head of the string."""
        self._emit_all(self._pop())
        self._context ^= contexts.TEMPLATE_PARAM_KEY
        self._context |= contexts.TEMPLATE_PARAM_VALUE
        self._emit(tokens.TemplateParamEquals())

    def _handle_template_end(self):
        """Handle the end of a template at the head of the string."""
        if self._context & contexts.TEMPLATE_NAME:
            if not self._context & (contexts.HAS_TEXT | contexts.HAS_TEMPLATE):
                self._fail_route()
        elif self._context & contexts.TEMPLATE_PARAM_KEY:
            self._emit_all(self._pop())
        self._head += 1
        return self._pop()

    def _handle_argument_separator(self):
        """Handle the separator between an argument's name and default."""
        self._context ^= contexts.ARGUMENT_NAME
        self._context |= contexts.ARGUMENT_DEFAULT
        self._emit(tokens.ArgumentSeparator())

    def _handle_argument_end(self):
        """Handle the end of an argument at the head of the string."""
        self._head += 2
        return self._pop()

    def _parse_wikilink(self):
        """Parse an internal wikilink at the head of the wikicode string."""
        reset = self._head + 1
        self._head += 2
        try:
            # If the wikilink looks like an external link, parse it as such:
            link, _extra, _delta = self._really_parse_external_link(True)
        except BadRoute:
            self._head = reset + 1
            try:
                # Otherwise, actually parse it as a wikilink:
                wikilink = self._parse(contexts.WIKILINK_TITLE)
            except BadRoute:
                self._head = reset
                self._emit_text("[[")
            else:
                self._emit(tokens.WikilinkOpen())
                self._emit_all(wikilink)
                self._emit(tokens.WikilinkClose())
        else:
            if self._context & contexts.EXT_LINK_TITLE:
                # In this exceptional case, an external link that looks like a
                # wikilink inside of an external link is parsed as text:
                self._head = reset
                self._emit_text("[[")
                return
            self._emit_text("[")
            self._emit(tokens.ExternalLinkOpen(brackets=True))
            self._emit_all(link)
            self._emit(tokens.ExternalLinkClose())

    def _handle_wikilink_separator(self):
        """Handle the separator between a wikilink's title and its text."""
        self._context ^= contexts.WIKILINK_TITLE
        self._context |= contexts.WIKILINK_TEXT
        self._emit(tokens.WikilinkSeparator())

    def _handle_wikilink_end(self):
        """Handle the end of a wikilink at the head of the string."""
        self._head += 1
        return self._pop()

    def _parse_bracketed_uri_scheme(self):
        """Parse the URI scheme of a bracket-enclosed external link."""
        self._push(contexts.EXT_LINK_URI)
        if self._read() == self._read(1) == "/":
            self._emit_text("//")
            self._head += 2
        else:
            valid = "abcdefghijklmnopqrstuvwxyz0123456789+.-"
            all_valid = lambda: all(char in valid for char in self._read())
            scheme = ""
            while self._read() is not self.END and all_valid():
                scheme += self._read()
                self._emit_text(self._read())
                self._head += 1
            if self._read() != ":":
                self._fail_route()
            self._emit_text(":")
            self._head += 1
            slashes = self._read() == self._read(1) == "/"
            if slashes:
                self._emit_text("//")
                self._head += 2
            if not is_scheme(scheme, slashes):
                self._fail_route()

    def _parse_free_uri_scheme(self):
        """Parse the URI scheme of a free (no brackets) external link."""
        valid = "abcdefghijklmnopqrstuvwxyz0123456789+.-"
        scheme = []
        try:
            # We have to backtrack through the textbuffer looking for our
            # scheme since it was just parsed as text:
            for chunk in reversed(self._textbuffer):
                for char in reversed(chunk):
                    if char.isspace() or char in self.MARKERS:
                        raise StopIteration()
                    if char not in valid:
                        raise BadRoute()
                    scheme.append(char)
        except StopIteration:
            pass
        scheme = "".join(reversed(scheme))
        slashes = self._read() == self._read(1) == "/"
        if not is_scheme(scheme, slashes):
            raise BadRoute()
        self._push(self._context | contexts.EXT_LINK_URI)
        self._emit_text(scheme)
        self._emit_text(":")
        if slashes:
            self._emit_text("//")
            self._head += 2

    def _handle_free_link_text(self, punct, tail, this):
        """Handle text in a free ext link, including trailing punctuation."""
        if "(" in this and ")" in punct:
            punct = punct[:-1]  # ')' is not longer valid punctuation
        if this.endswith(punct):
            for i in range(len(this) - 1, 0, -1):
                if this[i - 1] not in punct:
                    break
            else:
                i = 0
            stripped = this[:i]
            if stripped and tail:
                self._emit_text(tail)
                tail = ""
            tail += this[i:]
            this = stripped
        elif tail:
            self._emit_text(tail)
            tail = ""
        self._emit_text(this)
        return punct, tail

    def _is_free_link_end(self, this, nxt):
        """Return whether the current head is the end of a free link."""
        # Built from _parse()'s end sentinels:
        after, ctx = self._read(2), self._context
        equal_sign_contexts = contexts.TEMPLATE_PARAM_KEY | contexts.HEADING
        return (this in (self.END, "\n", "[", "]", "<", ">") or
                this == nxt == "'" or
                (this == "|" and ctx & contexts.TEMPLATE) or
                (this == "=" and ctx & equal_sign_contexts) or
                (this == nxt == "}" and ctx & contexts.TEMPLATE) or
                (this == nxt == after == "}" and ctx & contexts.ARGUMENT))

    def _really_parse_external_link(self, brackets):
        """Really parse an external link."""
        if brackets:
            self._parse_bracketed_uri_scheme()
            invalid = ("\n", " ", "]")
        else:
            self._parse_free_uri_scheme()
            invalid = ("\n", " ", "[", "]")
            punct = tuple(",;\\.:!?)")
        if self._read() is self.END or self._read()[0] in invalid:
            self._fail_route()
        tail = ""
        while True:
            this, nxt = self._read(), self._read(1)
            if this == "&":
                if tail:
                    self._emit_text(tail)
                    tail = ""
                self._parse_entity()
            elif (this == "<" and nxt == "!" and self._read(2) ==
                  self._read(3) == "-"):
                if tail:
                    self._emit_text(tail)
                    tail = ""
                self._parse_comment()
            elif not brackets and self._is_free_link_end(this, nxt):
                return self._pop(), tail, -1
            elif this is self.END or this == "\n":
                self._fail_route()
            elif this == nxt == "{" and self._can_recurse():
                if tail:
                    self._emit_text(tail)
                    tail = ""
                self._parse_template_or_argument()
            elif this == "]":
                return self._pop(), tail, 0
            elif " " in this:
                before, after = this.split(" ", 1)
                if brackets:
                    self._emit_text(before)
                    self._emit(tokens.ExternalLinkSeparator())
                    if after:
                        self._emit_text(after)
                    self._context ^= contexts.EXT_LINK_URI
                    self._context |= contexts.EXT_LINK_TITLE
                    self._head += 1
                    return self._parse(push=False), None, 0
                punct, tail = self._handle_free_link_text(punct, tail, before)
                return self._pop(), tail + " " + after, 0
            elif not brackets:
                punct, tail = self._handle_free_link_text(punct, tail, this)
            else:
                self._emit_text(this)
            self._head += 1

    def _remove_uri_scheme_from_textbuffer(self, scheme):
        """Remove the URI scheme of a new external link from the textbuffer."""
        length = len(scheme)
        while length:
            if length < len(self._textbuffer[-1]):
                self._textbuffer[-1] = self._textbuffer[-1][:-length]
                break
            length -= len(self._textbuffer[-1])
            self._textbuffer.pop()

    def _parse_external_link(self, brackets):
        """Parse an external link at the head of the wikicode string."""
        if self._context & contexts.NO_EXT_LINKS or not self._can_recurse():
            if not brackets and self._context & contexts.DL_TERM:
                self._handle_dl_term()
            else:
                self._emit_text(self._read())
            return

        reset = self._head
        self._head += 1
        try:
            link, extra, delta = self._really_parse_external_link(brackets)
        except BadRoute:
            self._head = reset
            if not brackets and self._context & contexts.DL_TERM:
                self._handle_dl_term()
            else:
                self._emit_text(self._read())
        else:
            if not brackets:
                scheme = link[0].text.split(":", 1)[0]
                self._remove_uri_scheme_from_textbuffer(scheme)
            self._emit(tokens.ExternalLinkOpen(brackets=brackets))
            self._emit_all(link)
            self._emit(tokens.ExternalLinkClose())
            self._head += delta
            if extra:
                self._emit_text(extra)

    def _parse_heading(self):
        """Parse a section heading at the head of the wikicode string."""
        self._global |= contexts.GL_HEADING
        reset = self._head
        self._head += 1
        best = 1
        while self._read() == "=":
            best += 1
            self._head += 1
        context = contexts.HEADING_LEVEL_1 << min(best - 1, 5)

        try:
            title, level = self._parse(context)
        except BadRoute:
            self._head = reset + best - 1
            self._emit_text("=" * best)
        else:
            self._emit(tokens.HeadingStart(level=level))
            if level < best:
                self._emit_text("=" * (best - level))
            self._emit_all(title)
            self._emit(tokens.HeadingEnd())
        finally:
            self._global ^= contexts.GL_HEADING

    def _handle_heading_end(self):
        """Handle the end of a section heading at the head of the string."""
        reset = self._head
        self._head += 1
        best = 1
        while self._read() == "=":
            best += 1
            self._head += 1
        current = int(log(self._context / contexts.HEADING_LEVEL_1, 2)) + 1
        level = min(current, min(best, 6))

        try:  # Try to check for a heading closure after this one
            after, after_level = self._parse(self._context)
        except BadRoute:
            if level < best:
                self._emit_text("=" * (best - level))
            self._head = reset + best - 1
            return self._pop(), level
        else:  # Found another closure
            self._emit_text("=" * best)
            self._emit_all(after)
            return self._pop(), after_level

    def _really_parse_entity(self):
        """Actually parse an HTML entity and ensure that it is valid."""
        self._emit(tokens.HTMLEntityStart())
        self._head += 1

        this = self._read(strict=True)
        if this == "#":
            numeric = True
            self._emit(tokens.HTMLEntityNumeric())
            self._head += 1
            this = self._read(strict=True)
            if this[0].lower() == "x":
                hexadecimal = True
                self._emit(tokens.HTMLEntityHex(char=this[0]))
                this = this[1:]
                if not this:
                    self._fail_route()
            else:
                hexadecimal = False
        else:
            numeric = hexadecimal = False

        valid = "0123456789abcdefABCDEF" if hexadecimal else "0123456789"
        if not numeric and not hexadecimal:
            valid += "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
        if not all([char in valid for char in this]):
            self._fail_route()

        self._head += 1
        if self._read() != ";":
            self._fail_route()
        if numeric:
            test = int(this, 16) if hexadecimal else int(this)
            if test < 1 or test > 0x10FFFF:
                self._fail_route()
        else:
            if this not in htmlentities.entitydefs:
                self._fail_route()

        self._emit(tokens.Text(text=this))
        self._emit(tokens.HTMLEntityEnd())

    def _parse_entity(self):
        """Parse an HTML entity at the head of the wikicode string."""
        reset = self._head
        try:
            self._push(contexts.HTML_ENTITY)
            self._really_parse_entity()
        except BadRoute:
            self._head = reset
            self._emit_text(self._read())
        else:
            self._emit_all(self._pop())

    def _parse_comment(self):
        """Parse an HTML comment at the head of the wikicode string."""
        self._head += 4
        reset = self._head - 1
        self._push()
        while True:
            this = self._read()
            if this == self.END:
                self._pop()
                self._head = reset
                self._emit_text("<!--")
                return
            if this == self._read(1) == "-" and self._read(2) == ">":
                self._emit_first(tokens.CommentStart())
                self._emit(tokens.CommentEnd())
                self._emit_all(self._pop())
                self._head += 2
                if self._context & contexts.FAIL_NEXT:
                    # _verify_safe() sets this flag while parsing a template
                    # or link when it encounters what might be a comment -- we
                    # must unset it to let _verify_safe() know it was correct:
                    self._context ^= contexts.FAIL_NEXT
                return
            self._emit_text(this)
            self._head += 1

    def _push_tag_buffer(self, data):
        """Write a pending tag attribute from *data* to the stack."""
        if data.context & data.CX_QUOTED:
            self._emit_first(tokens.TagAttrQuote(char=data.quoter))
            self._emit_all(self._pop())
        buf = data.padding_buffer
        self._emit_first(tokens.TagAttrStart(
            pad_first=buf["first"], pad_before_eq=buf["before_eq"],
            pad_after_eq=buf["after_eq"]))
        self._emit_all(self._pop())
        for key in data.padding_buffer:
            data.padding_buffer[key] = ""

    def _handle_tag_space(self, data, text):
        """Handle whitespace (*text*) inside of an HTML open tag."""
        ctx = data.context
        end_of_value = ctx & data.CX_ATTR_VALUE and not ctx & (data.CX_QUOTED | data.CX_NOTE_QUOTE)
        if end_of_value or (ctx & data.CX_QUOTED and ctx & data.CX_NOTE_SPACE):
            self._push_tag_buffer(data)
            data.context = data.CX_ATTR_READY
        elif ctx & data.CX_NOTE_SPACE:
            data.context = data.CX_ATTR_READY
        elif ctx & data.CX_ATTR_NAME:
            data.context |= data.CX_NOTE_EQUALS
            data.padding_buffer["before_eq"] += text
        if ctx & data.CX_QUOTED and not ctx & data.CX_NOTE_SPACE:
            self._emit_text(text)
        elif data.context & data.CX_ATTR_READY:
            data.padding_buffer["first"] += text
        elif data.context & data.CX_ATTR_VALUE:
            data.padding_buffer["after_eq"] += text

    def _handle_tag_text(self, text):
        """Handle regular *text* inside of an HTML open tag."""
        nxt = self._read(1)
        if not self._can_recurse() or text not in self.MARKERS:
            self._emit_text(text)
        elif text == nxt == "{":
            self._parse_template_or_argument()
        elif text == nxt == "[":
            self._parse_wikilink()
        elif text == "<":
            self._parse_tag()
        else:
            self._emit_text(text)

    def _handle_tag_data(self, data, text):
        """Handle all sorts of *text* data inside of an HTML open tag."""
        for chunk in self.tag_splitter.split(text):
            if not chunk:
                continue
            if data.context & data.CX_NAME:
                if chunk in self.MARKERS or chunk.isspace():
                    self._fail_route()  # Tags must start with text, not spaces
                data.context = data.CX_NOTE_SPACE
            elif chunk.isspace():
                self._handle_tag_space(data, chunk)
                continue
            elif data.context & data.CX_NOTE_SPACE:
                if data.context & data.CX_QUOTED:
                    data.context = data.CX_ATTR_VALUE
                    self._memoize_bad_route()
                    self._pop()
                    self._head = data.reset - 1  # Will be auto-incremented
                    return  # Break early
                self._fail_route()
            elif data.context & data.CX_ATTR_READY:
                data.context = data.CX_ATTR_NAME
                self._push(contexts.TAG_ATTR)
            elif data.context & data.CX_ATTR_NAME:
                if chunk == "=":
                    data.context = data.CX_ATTR_VALUE | data.CX_NOTE_QUOTE
                    self._emit(tokens.TagAttrEquals())
                    continue
                if data.context & data.CX_NOTE_EQUALS:
                    self._push_tag_buffer(data)
                    data.context = data.CX_ATTR_NAME
                    self._push(contexts.TAG_ATTR)
            else:  # data.context & data.CX_ATTR_VALUE assured
                escaped = self._read(-1) == "\\" and self._read(-2) != "\\"
                if data.context & data.CX_NOTE_QUOTE:
                    data.context ^= data.CX_NOTE_QUOTE
                    if chunk in "'\"" and not escaped:
                        data.context |= data.CX_QUOTED
                        data.quoter = chunk
                        data.reset = self._head
                        try:
                            self._push(self._context)
                        except BadRoute:
                            # Already failed to parse this as a quoted string
                            data.context = data.CX_ATTR_VALUE
                            self._head -= 1
                            return
                        continue
                elif data.context & data.CX_QUOTED:
                    if chunk == data.quoter and not escaped:
                        data.context |= data.CX_NOTE_SPACE
                        continue
            self._handle_tag_text(chunk)

    def _handle_tag_close_open(self, data, token):
        """Handle the closing of a open tag (``<foo>``)."""
        if data.context & (data.CX_ATTR_NAME | data.CX_ATTR_VALUE):
            self._push_tag_buffer(data)
        self._emit(token(padding=data.padding_buffer["first"]))
        self._head += 1

    def _handle_tag_open_close(self):
        """Handle the opening of a closing tag (``</foo>``)."""
        self._emit(tokens.TagOpenClose())
        self._push(contexts.TAG_CLOSE)
        self._head += 1

    def _handle_tag_close_close(self):
        """Handle the ending of a closing tag (``</foo>``)."""
        strip = lambda tok: tok.text.rstrip().lower()
        closing = self._pop()
        if len(closing) != 1 or (not isinstance(closing[0], tokens.Text) or
                                 strip(closing[0]) != strip(self._stack[1])):
            self._fail_route()
        self._emit_all(closing)
        self._emit(tokens.TagCloseClose())
        return self._pop()

    def _handle_blacklisted_tag(self):
        """Handle the body of an HTML tag that is parser-blacklisted."""
        strip = lambda text: text.rstrip().lower()
        while True:
            this, nxt = self._read(), self._read(1)
            if this is self.END:
                self._fail_route()
            elif this == "<" and nxt == "/":
                self._head += 3
                if self._read() != ">" or (strip(self._read(-1)) !=
                                           strip(self._stack[1].text)):
                    self._head -= 1
                    self._emit_text("</")
                    continue
                self._emit(tokens.TagOpenClose())
                self._emit_text(self._read(-1))
                self._emit(tokens.TagCloseClose())
                return self._pop()
            elif this == "&":
                self._parse_entity()
            else:
                self._emit_text(this)
            self._head += 1

    def _handle_single_only_tag_end(self):
        """Handle the end of an implicitly closing single-only HTML tag."""
        padding = self._stack.pop().padding
        self._emit(tokens.TagCloseSelfclose(padding=padding, implicit=True))
        self._head -= 1  # Offset displacement done by _handle_tag_close_open
        return self._pop()

    def _handle_single_tag_end(self):
        """Handle the stream end when inside a single-supporting HTML tag."""
        stack = self._stack
        # We need to find the index of the TagCloseOpen token corresponding to
        # the TagOpenOpen token located at index 0:
        depth = 1
        for index, token in enumerate(stack[2:], 2):
            if isinstance(token, tokens.TagOpenOpen):
                depth += 1
            elif isinstance(token, tokens.TagCloseOpen):
                depth -= 1
                if depth == 0:
                    break
            elif isinstance(token, tokens.TagCloseSelfclose):
                depth -= 1
                if depth == 0:  # pragma: no cover (untestable/exceptional)
                    raise ParserError(
                        "_handle_single_tag_end() got an unexpected "
                        "TagCloseSelfclose")
        else:  # pragma: no cover (untestable/exceptional case)
            raise ParserError("_handle_single_tag_end() missed a TagCloseOpen")
        padding = stack[index].padding
        stack[index] = tokens.TagCloseSelfclose(padding=padding, implicit=True)
        return self._pop()

    def _really_parse_tag(self):
        """Actually parse an HTML tag, starting with the open (``<foo>``)."""
        data = _TagOpenData()
        self._push(contexts.TAG_OPEN)
        self._emit(tokens.TagOpenOpen())
        while True:
            this, nxt = self._read(), self._read(1)
            can_exit = (not data.context & (data.CX_QUOTED | data.CX_NAME) or
                        data.context & data.CX_NOTE_SPACE)
            if this is self.END:
                if self._context & contexts.TAG_ATTR:
                    if data.context & data.CX_QUOTED:
                        # Unclosed attribute quote: reset, don't die
                        data.context = data.CX_ATTR_VALUE
                        self._memoize_bad_route()
                        self._pop()
                        self._head = data.reset
                        continue
                    self._pop()
                self._fail_route()
            elif this == ">" and can_exit:
                self._handle_tag_close_open(data, tokens.TagCloseOpen)
                self._context = contexts.TAG_BODY
                if is_single_only(self._stack[1].text):
                    return self._handle_single_only_tag_end()
                if is_parsable(self._stack[1].text):
                    return self._parse(push=False)
                return self._handle_blacklisted_tag()
            elif this == "/" and nxt == ">" and can_exit:
                self._handle_tag_close_open(data, tokens.TagCloseSelfclose)
                return self._pop()
            else:
                self._handle_tag_data(data, this)
            self._head += 1

    def _handle_invalid_tag_start(self):
        """Handle the (possible) start of an implicitly closing single tag."""
        reset = self._head + 1
        self._head += 2
        try:
            if not is_single_only(self.tag_splitter.split(self._read())[0]):
                raise BadRoute()
            tag = self._really_parse_tag()
        except BadRoute:
            self._head = reset
            self._emit_text("</")
        else:
            tag[0].invalid = True  # Set flag of TagOpenOpen
            self._emit_all(tag)

    def _parse_tag(self):
        """Parse an HTML tag at the head of the wikicode string."""
        reset = self._head
        self._head += 1
        try:
            tag = self._really_parse_tag()
        except BadRoute:
            self._head = reset
            self._emit_text("<")
        else:
            self._emit_all(tag)

    def _emit_style_tag(self, tag, markup, body):
        """Write the body of a tag and the tokens that should surround it."""
        self._emit(tokens.TagOpenOpen(wiki_markup=markup))
        self._emit_text(tag)
        self._emit(tokens.TagCloseOpen())
        self._emit_all(body)
        self._emit(tokens.TagOpenClose())
        self._emit_text(tag)
        self._emit(tokens.TagCloseClose())

    def _parse_italics(self):
        """Parse wiki-style italics."""
        reset = self._head
        try:
            stack = self._parse(contexts.STYLE_ITALICS)
        except BadRoute as route:
            self._head = reset
            if route.context & contexts.STYLE_PASS_AGAIN:
                new_ctx = contexts.STYLE_ITALICS | contexts.STYLE_SECOND_PASS
                try:
                    stack = self._parse(new_ctx)
                except BadRoute:
                    self._head = reset
                    self._emit_text("''")
                    return
            else:
                self._emit_text("''")
                return
        self._emit_style_tag("i", "''", stack)

    def _parse_bold(self):
        """Parse wiki-style bold."""
        reset = self._head
        try:
            stack = self._parse(contexts.STYLE_BOLD)
        except BadRoute:
            self._head = reset
            if self._context & contexts.STYLE_SECOND_PASS:
                self._emit_text("'")
                return True
            if self._context & contexts.STYLE_ITALICS:
                self._context |= contexts.STYLE_PASS_AGAIN
                self._emit_text("'''")
            else:
                self._emit_text("'")
                self._parse_italics()
        else:
            self._emit_style_tag("b", "'''", stack)
        return False

    def _parse_italics_and_bold(self):
        """Parse wiki-style italics and bold together (i.e., five ticks)."""
        reset = self._head
        try:
            stack = self._parse(contexts.STYLE_BOLD)
        except BadRoute:
            self._head = reset
            try:
                stack = self._parse(contexts.STYLE_ITALICS)
            except BadRoute:
                self._head = reset
                self._emit_text("'''''")
            else:
                reset = self._head
                try:
                    stack2 = self._parse(contexts.STYLE_BOLD)
                except BadRoute:
                    self._head = reset
                    self._emit_text("'''")
                    self._emit_style_tag("i", "''", stack)
                else:
                    self._push()
                    self._emit_style_tag("i", "''", stack)
                    self._emit_all(stack2)
                    self._emit_style_tag("b", "'''", self._pop())
        else:
            reset = self._head
            try:
                stack2 = self._parse(contexts.STYLE_ITALICS)
            except BadRoute:
                self._head = reset
                self._emit_text("''")
                self._emit_style_tag("b", "'''", stack)
            else:
                self._push()
                self._emit_style_tag("b", "'''", stack)
                self._emit_all(stack2)
                self._emit_style_tag("i", "''", self._pop())

    def _parse_style(self):
        """Parse wiki-style formatting (``''``/``'''`` for italics/bold)."""
        self._head += 2
        ticks = 2
        while self._read() == "'":
            self._head += 1
            ticks += 1
        italics = self._context & contexts.STYLE_ITALICS
        bold = self._context & contexts.STYLE_BOLD

        if ticks > 5:
            self._emit_text("'" * (ticks - 5))
            ticks = 5
        elif ticks == 4:
            self._emit_text("'")
            ticks = 3

        if (italics and ticks in (2, 5)) or (bold and ticks in (3, 5)):
            if ticks == 5:
                self._head -= 3 if italics else 2
            return self._pop()
        if not self._can_recurse():
            if ticks == 3:
                if self._context & contexts.STYLE_SECOND_PASS:
                    self._emit_text("'")
                    return self._pop()
                if self._context & contexts.STYLE_ITALICS:
                    self._context |= contexts.STYLE_PASS_AGAIN
            self._emit_text("'" * ticks)
        elif ticks == 2:
            self._parse_italics()
        elif ticks == 3:
            if self._parse_bold():
                return self._pop()
        else:  # ticks == 5
            self._parse_italics_and_bold()
        self._head -= 1

    def _handle_list_marker(self):
        """Handle a list marker at the head (``#``, ``*``, ``;``, ``:``)."""
        markup = self._read()
        if markup == ";":
            self._context |= contexts.DL_TERM
        self._emit(tokens.TagOpenOpen(wiki_markup=markup))
        self._emit_text(get_html_tag(markup))
        self._emit(tokens.TagCloseSelfclose())

    def _handle_list(self):
        """Handle a wiki-style list (``#``, ``*``, ``;``, ``:``)."""
        self._handle_list_marker()
        while self._read(1) in ("#", "*", ";", ":"):
            self._head += 1
            self._handle_list_marker()

    def _handle_hr(self):
        """Handle a wiki-style horizontal rule (``----``) in the string."""
        length = 4
        self._head += 3
        while self._read(1) == "-":
            length += 1
            self._head += 1
        self._emit(tokens.TagOpenOpen(wiki_markup="-" * length))
        self._emit_text("hr")
        self._emit(tokens.TagCloseSelfclose())

    def _handle_dl_term(self):
        """Handle the term in a description list (``foo`` in ``;foo:bar``)."""
        self._context ^= contexts.DL_TERM
        if self._read() == ":":
            self._handle_list_marker()
        else:
            self._emit_text("\n")

    def _emit_table_tag(self, open_open_markup, tag, style, padding,
                        close_open_markup, contents, open_close_markup):
        """Emit a table tag."""
        self._emit(tokens.TagOpenOpen(wiki_markup=open_open_markup))
        self._emit_text(tag)
        if style:
            self._emit_all(style)
        if close_open_markup:
            self._emit(tokens.TagCloseOpen(wiki_markup=close_open_markup,
                                           padding=padding))
        else:
            self._emit(tokens.TagCloseOpen(padding=padding))
        if contents:
            self._emit_all(contents)
        self._emit(tokens.TagOpenClose(wiki_markup=open_close_markup))
        self._emit_text(tag)
        self._emit(tokens.TagCloseClose())

    def _handle_table_style(self, end_token):
        """Handle style attributes for a table until ``end_token``."""
        data = _TagOpenData()
        data.context = _TagOpenData.CX_ATTR_READY
        while True:
            this = self._read()
            can_exit = (not data.context & data.CX_QUOTED or
                        data.context & data.CX_NOTE_SPACE)
            if this == end_token and can_exit:
                if data.context & (data.CX_ATTR_NAME | data.CX_ATTR_VALUE):
                    self._push_tag_buffer(data)
                if this.isspace():
                    data.padding_buffer["first"] += this
                return data.padding_buffer["first"]
            if this is self.END or this == end_token:
                if self._context & contexts.TAG_ATTR:
                    if data.context & data.CX_QUOTED:
                        # Unclosed attribute quote: reset, don't die
                        data.context = data.CX_ATTR_VALUE
                        self._memoize_bad_route()
                        self._pop()
                        self._head = data.reset
                        continue
                    self._pop()
                self._fail_route()
            else:
                self._handle_tag_data(data, this)
            self._head += 1

    def _parse_table(self):
        """Parse a wikicode table by starting with the first line."""
        reset = self._head
        self._head += 2
        try:
            self._push(contexts.TABLE_OPEN)
            padding = self._handle_table_style("\n")
        except BadRoute:
            self._head = reset
            self._emit_text("{")
            return
        style = self._pop()

        self._head += 1
        restore_point = self._stack_ident
        try:
            table = self._parse(contexts.TABLE_OPEN)
        except BadRoute:
            while self._stack_ident != restore_point:
                self._memoize_bad_route()
                self._pop()
            self._head = reset
            self._emit_text("{")
            return

        self._emit_table_tag("{|", "table", style, padding, None, table, "|}")
        # Offset displacement done by _parse():
        self._head -= 1

    def _handle_table_row(self):
        """Parse as style until end of the line, then continue."""
        self._head += 2
        if not self._can_recurse():
            self._emit_text("|-")
            self._head -= 1
            return

        self._push(contexts.TABLE_OPEN | contexts.TABLE_ROW_OPEN)
        padding = self._handle_table_style("\n")
        style = self._pop()

        # Don't parse the style separator:
        self._head += 1
        row = self._parse(contexts.TABLE_OPEN | contexts.TABLE_ROW_OPEN)

        self._emit_table_tag("|-", "tr", style, padding, None, row, "")
        # Offset displacement done by parse():
        self._head -= 1

    def _handle_table_cell(self, markup, tag, line_context):
        """Parse as normal syntax unless we hit a style marker, then parse
        style as HTML attributes and the remainder as normal syntax."""
        old_context = self._context
        padding, style = "", None
        self._head += len(markup)
        reset = self._head
        if not self._can_recurse():
            self._emit_text(markup)
            self._head -= 1
            return

        cell = self._parse(contexts.TABLE_OPEN | contexts.TABLE_CELL_OPEN |
                           line_context | contexts.TABLE_CELL_STYLE)
        cell_context = self._context
        self._context = old_context
        reset_for_style = cell_context & contexts.TABLE_CELL_STYLE
        if reset_for_style:
            self._head = reset
            self._push(contexts.TABLE_OPEN | contexts.TABLE_CELL_OPEN |
                       line_context)
            padding = self._handle_table_style("|")
            style = self._pop()
            # Don't parse the style separator:
            self._head += 1
            cell = self._parse(contexts.TABLE_OPEN | contexts.TABLE_CELL_OPEN |
                               line_context)
            cell_context = self._context
            self._context = old_context

        close_open_markup = "|" if reset_for_style else None
        self._emit_table_tag(markup, tag, style, padding, close_open_markup,
                             cell, "")
        # Keep header/cell line contexts:
        self._context |= cell_context & (contexts.TABLE_TH_LINE |
                                         contexts.TABLE_TD_LINE)
        # Offset displacement done by parse():
        self._head -= 1

    def _handle_table_cell_end(self, reset_for_style=False):
        """Returns the current context, with the TABLE_CELL_STYLE flag set if
        it is necessary to reset and parse style attributes."""
        if reset_for_style:
            self._context |= contexts.TABLE_CELL_STYLE
        else:
            self._context &= ~contexts.TABLE_CELL_STYLE
        return self._pop(keep_context=True)

    def _handle_table_row_end(self):
        """Return the stack in order to handle the table row end."""
        return self._pop()

    def _handle_table_end(self):
        """Return the stack in order to handle the table end."""
        self._head += 2
        return self._pop()

    def _handle_end(self):
        """Handle the end of the stream of wikitext."""
        if self._context & contexts.FAIL:
            if self._context & contexts.TAG_BODY:
                if is_single(self._stack[1].text):
                    return self._handle_single_tag_end()
            if self._context & contexts.TABLE_CELL_OPEN:
                self._pop()
            if self._context & contexts.DOUBLE:
                self._pop()
            self._fail_route()
        return self._pop()

    def _verify_safe(self, this):
        """Make sure we are not trying to write an invalid character."""
        context = self._context
        if context & contexts.FAIL_NEXT:
            return False
        if context & contexts.WIKILINK_TITLE:
            if this in ("]", "{"):
                self._context |= contexts.FAIL_NEXT
            elif this in ("\n", "[", "}", ">"):
                return False
            elif this == "<":
                if self._read(1) == "!":
                    self._context |= contexts.FAIL_NEXT
                else:
                    return False
            return True
        if context & contexts.EXT_LINK_TITLE:
            return this != "\n"
        if context & contexts.TEMPLATE_NAME:
            if this == "{":
                self._context |= contexts.HAS_TEMPLATE | contexts.FAIL_NEXT
                return True
            if this == "}" or (this == "<" and self._read(1) == "!"):
                self._context |= contexts.FAIL_NEXT
                return True
            if this in ("[", "]", "<", ">"):
                return False
            if this == "|":
                return True
            if context & contexts.HAS_TEXT:
                if context & contexts.FAIL_ON_TEXT:
                    if this is self.END or not this.isspace():
                        return False
                elif this == "\n":
                    self._context |= contexts.FAIL_ON_TEXT
            elif this is self.END or not this.isspace():
                self._context |= contexts.HAS_TEXT
            return True
        if context & contexts.TAG_CLOSE:
            return this != "<"
        if context & contexts.FAIL_ON_EQUALS:
            if this == "=":
                return False
        elif context & contexts.FAIL_ON_LBRACE:
            if this == "{" or (self._read(-1) == self._read(-2) == "{"):
                if context & contexts.TEMPLATE:
                    self._context |= contexts.FAIL_ON_EQUALS
                else:
                    self._context |= contexts.FAIL_NEXT
                return True
            self._context ^= contexts.FAIL_ON_LBRACE
        elif context & contexts.FAIL_ON_RBRACE:
            if this == "}":
                self._context |= contexts.FAIL_NEXT
                return True
            self._context ^= contexts.FAIL_ON_RBRACE
        elif this == "{":
            self._context |= contexts.FAIL_ON_LBRACE
        elif this == "}":
            self._context |= contexts.FAIL_ON_RBRACE
        return True

    def _parse(self, context=0, push=True):
        """Parse the wikicode string, using *context* for when to stop."""
        if push:
            self._push(context)
        while True:
            this = self._read()
            if self._context & contexts.UNSAFE:
                if not self._verify_safe(this):
                    if self._context & contexts.DOUBLE:
                        self._pop()
                    self._fail_route()
            if this not in self.MARKERS:
                self._emit_text(this)
                self._head += 1
                continue
            if this is self.END:
                return self._handle_end()
            nxt = self._read(1)
            if this == nxt == "{":
                if self._can_recurse():
                    self._parse_template_or_argument()
                else:
                    self._emit_text("{")
            elif this == "|" and self._context & contexts.TEMPLATE:
                self._handle_template_param()
            elif this == "=" and self._context & contexts.TEMPLATE_PARAM_KEY:
                self._handle_template_param_value()
            elif this == nxt == "}" and self._context & contexts.TEMPLATE:
                return self._handle_template_end()
            elif this == "|" and self._context & contexts.ARGUMENT_NAME:
                self._handle_argument_separator()
            elif this == nxt == "}" and self._context & contexts.ARGUMENT:
                if self._read(2) == "}":
                    return self._handle_argument_end()
                self._emit_text("}")
            elif this == nxt == "[" and self._can_recurse():
                if not self._context & contexts.NO_WIKILINKS:
                    self._parse_wikilink()
                else:
                    self._emit_text("[")
            elif this == "|" and self._context & contexts.WIKILINK_TITLE:
                self._handle_wikilink_separator()
            elif this == nxt == "]" and self._context & contexts.WIKILINK:
                return self._handle_wikilink_end()
            elif this == "[":
                self._parse_external_link(True)
            elif this == ":" and self._read(-1) not in self.MARKERS:
                self._parse_external_link(False)
            elif this == "]" and self._context & contexts.EXT_LINK_TITLE:
                return self._pop()
            elif this == "=" and not self._global & contexts.GL_HEADING:
                if self._read(-1) in ("\n", self.START):
                    self._parse_heading()
                else:
                    self._emit_text("=")
            elif this == "=" and self._context & contexts.HEADING:
                return self._handle_heading_end()
            elif this == "\n" and self._context & contexts.HEADING:
                self._fail_route()
            elif this == "&":
                self._parse_entity()
            elif this == "<" and nxt == "!":
                if self._read(2) == self._read(3) == "-":
                    self._parse_comment()
                else:
                    self._emit_text(this)
            elif this == "<" and nxt == "/" and self._read(2) is not self.END:
                if self._context & contexts.TAG_BODY:
                    self._handle_tag_open_close()
                else:
                    self._handle_invalid_tag_start()
            elif this == "<" and not self._context & contexts.TAG_CLOSE:
                if self._can_recurse():
                    self._parse_tag()
                else:
                    self._emit_text("<")
            elif this == ">" and self._context & contexts.TAG_CLOSE:
                return self._handle_tag_close_close()
            elif this == nxt == "'" and not self._skip_style_tags:
                result = self._parse_style()
                if result is not None:
                    return result
            elif self._read(-1) in ("\n", self.START) and this in ("#", "*", ";", ":"):
                self._handle_list()
            elif self._read(-1) in ("\n", self.START) and (
                    this == nxt == self._read(2) == self._read(3) == "-"):
                self._handle_hr()
            elif this in ("\n", ":") and self._context & contexts.DL_TERM:
                self._handle_dl_term()
                if this == "\n":
                    # Kill potential table contexts
                    self._context &= ~contexts.TABLE_CELL_LINE_CONTEXTS
            # Start of table parsing
            elif this == "{" and nxt == "|" and (
                    self._read(-1) in ("\n", self.START) or
                    (self._read(-2) in ("\n", self.START) and self._read(-1).isspace())):
                if self._can_recurse():
                    self._parse_table()
                else:
                    self._emit_text("{")
            elif self._context & contexts.TABLE_OPEN:
                if this == nxt == "|" and self._context & contexts.TABLE_TD_LINE:
                    if self._context & contexts.TABLE_CELL_OPEN:
                        return self._handle_table_cell_end()
                    self._handle_table_cell("||", "td", contexts.TABLE_TD_LINE)
                elif this == nxt == "|" and self._context & contexts.TABLE_TH_LINE:
                    if self._context & contexts.TABLE_CELL_OPEN:
                        return self._handle_table_cell_end()
                    self._handle_table_cell("||", "th", contexts.TABLE_TH_LINE)
                elif this == nxt == "!" and self._context & contexts.TABLE_TH_LINE:
                    if self._context & contexts.TABLE_CELL_OPEN:
                        return self._handle_table_cell_end()
                    self._handle_table_cell("!!", "th", contexts.TABLE_TH_LINE)
                elif this == "|" and self._context & contexts.TABLE_CELL_STYLE:
                    return self._handle_table_cell_end(reset_for_style=True)
                # on newline, clear out cell line contexts
                elif this == "\n" and self._context & contexts.TABLE_CELL_LINE_CONTEXTS:
                    self._context &= ~contexts.TABLE_CELL_LINE_CONTEXTS
                    self._emit_text(this)
                elif (self._read(-1) in ("\n", self.START) or
                      (self._read(-2) in ("\n", self.START) and self._read(-1).isspace())):
                    if this == "|" and nxt == "}":
                        if self._context & contexts.TABLE_CELL_OPEN:
                            return self._handle_table_cell_end()
                        if self._context & contexts.TABLE_ROW_OPEN:
                            return self._handle_table_row_end()
                        return self._handle_table_end()
                    if this == "|" and nxt == "-":
                        if self._context & contexts.TABLE_CELL_OPEN:
                            return self._handle_table_cell_end()
                        if self._context & contexts.TABLE_ROW_OPEN:
                            return self._handle_table_row_end()
                        self._handle_table_row()
                    elif this == "|":
                        if self._context & contexts.TABLE_CELL_OPEN:
                            return self._handle_table_cell_end()
                        self._handle_table_cell("|", "td", contexts.TABLE_TD_LINE)
                    elif this == "!":
                        if self._context & contexts.TABLE_CELL_OPEN:
                            return self._handle_table_cell_end()
                        self._handle_table_cell("!", "th", contexts.TABLE_TH_LINE)
                    else:
                        self._emit_text(this)
                else:
                    self._emit_text(this)

            else:
                self._emit_text(this)
            self._head += 1

    def tokenize(self, text, context=0, skip_style_tags=False):
        """Build a list of tokens from a string of wikicode and return it."""
        split = self.regex.split(text)
        self._text = [segment for segment in split if segment]
        self._head = self._global = self._depth = 0
        self._bad_routes = set()
        self._skip_style_tags = skip_style_tags

        try:
            result = self._parse(context)
        except BadRoute as exc:  # pragma: no cover (untestable/exceptional case)
            raise ParserError("Python tokenizer exited with BadRoute") from exc
        if self._stacks:  # pragma: no cover (untestable/exceptional case)
            err = "Python tokenizer exited with non-empty token stack"
            raise ParserError(err)
        return result