lxml.html.clean

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# Source Code for Module lxml.html.clean

      1  """A cleanup tool for HTML.
      2
      3  Removes unwanted tags and content.  See the `Cleaner` class for
      4  details.
      5  """
      6
      7  import re
      8  import copy
      9  try:
     10      from urlparse import urlsplit
     11  except ImportError:
     12      # Python 3
     13      from urllib.parse import urlsplit
     14  from lxml import etree
     15  from lxml.html import defs
     16  from lxml.html import fromstring, tostring, XHTML_NAMESPACE
     17  from lxml.html import xhtml_to_html, _transform_result
     18
     19  try:
     20      unichr
     21  except NameError:
     22      # Python 3
     23      unichr = chr
     24  try:
     25      unicode
     26  except NameError:
     27      # Python 3
     28      unicode = str
     29  try:
     30      bytes
     31  except NameError:
     32      # Python < 2.6
     33      bytes = str
     34  try:
     35      basestring
     36  except NameError:
     37      basestring = (str, bytes)
     38
     39
     40  __all__ = ['clean_html', 'clean', 'Cleaner', 'autolink', 'autolink_html',
     41             'word_break', 'word_break_html']
     42
     43  # Look at http://code.sixapart.com/trac/livejournal/browser/trunk/cgi-bin/cleanhtml.pl
     44  #   Particularly the CSS cleaning; most of the tag cleaning is integrated now
     45  # I have multiple kinds of schemes searched; but should schemes be
     46  #   whitelisted instead?
     47  # max height?
     48  # remove images?  Also in CSS?  background attribute?
     49  # Some way to whitelist object, iframe, etc (e.g., if you want to
     50  #   allow *just* embedded YouTube movies)
     51  # Log what was deleted and why?
     52  # style="behavior: ..." might be bad in IE?
     53  # Should we have something for just <meta http-equiv>?  That's the worst of the
     54  #   metas.
     55  # UTF-7 detections?  Example:
     56  #     <HEAD><META HTTP-EQUIV="CONTENT-TYPE" CONTENT="text/html; charset=UTF-7"> </HEAD>+ADw-SCRIPT+AD4-alert('XSS');+ADw-/SCRIPT+AD4-
     57  #   you don't always have to have the charset set, if the page has no charset
     58  #   and there's UTF7-like code in it.
     59  # Look at these tests: http://htmlpurifier.org/live/smoketests/xssAttacks.php
     60
     61
     62  # This is an IE-specific construct you can have in a stylesheet to
     63  # run some Javascript:
     64  _css_javascript_re = re.compile(
     65      r'expression\s*\(.*?\)', re.S|re.I)
     66
     67  # Do I have to worry about @\nimport?
     68  _css_import_re = re.compile(
     69      r'@\s*import', re.I)
     70
     71  # All kinds of schemes besides just javascript: that can cause
     72  # execution:
     73  _is_javascript_scheme = re.compile(
     74      r'(?:javascript|jscript|livescript|vbscript|data|about|mocha):',
     75      re.I).search
     76  _substitute_whitespace = re.compile(r'[\s\x00-\x08\x0B\x0C\x0E-\x19]+').sub
     77  # FIXME: should data: be blocked?
     78
     79  # FIXME: check against: http://msdn2.microsoft.com/en-us/library/ms537512.aspx
     80  _conditional_comment_re = re.compile(
     81      r'\[if[\s\n\r]+.*?][\s\n\r]*>', re.I|re.S)
     82
     83  _find_styled_elements = etree.XPath(
     84      "descendant-or-self::*[@style]")
     85
     86  _find_external_links = etree.XPath(
     87      ("descendant-or-self::a  [normalize-space(@href) and substring(normalize-space(@href),1,1) != '#'] |"
     88       "descendant-or-self::x:a[normalize-space(@href) and substring(normalize-space(@href),1,1) != '#']"),
     89      namespaces={'x':XHTML_NAMESPACE})
     90
     91 -class Cleaner(object):
     92      """
     93      Instances cleans the document of each of the possible offending
     94      elements.  The cleaning is controlled by attributes; you can
     95      override attributes in a subclass, or set them in the constructor.
     96
     97      ``scripts``:
     98          Removes any ``<script>`` tags.
     99
    100      ``javascript``:
    101          Removes any Javascript, like an ``onclick`` attribute. Also removes stylesheets
    102          as they could contain Javascript.
    103
    104      ``comments``:
    105          Removes any comments.
    106
    107      ``style``:
    108          Removes any style tags or attributes.
    109
    110      ``links``:
    111          Removes any ``<link>`` tags
    112
    113      ``meta``:
    114          Removes any ``<meta>`` tags
    115
    116      ``page_structure``:
    117          Structural parts of a page: ``<head>``, ``<html>``, ``<title>``.
    118
    119      ``processing_instructions``:
    120          Removes any processing instructions.
    121
    122      ``embedded``:
    123          Removes any embedded objects (flash, iframes)
    124
    125      ``frames``:
    126          Removes any frame-related tags
    127
    128      ``forms``:
    129          Removes any form tags
    130
    131      ``annoying_tags``:
    132          Tags that aren't *wrong*, but are annoying.  ``<blink>`` and ``<marquee>``
    133
    134      ``remove_tags``:
    135          A list of tags to remove.  Only the tags will be removed,
    136          their content will get pulled up into the parent tag.
    137
    138      ``kill_tags``:
    139          A list of tags to kill.  Killing also removes the tag's content,
    140          i.e. the whole subtree, not just the tag itself.
    141
    142      ``allow_tags``:
    143          A list of tags to include (default include all).
    144
    145      ``remove_unknown_tags``:
    146          Remove any tags that aren't standard parts of HTML.
    147
    148      ``safe_attrs_only``:
    149          If true, only include 'safe' attributes (specifically the list
    150          from the feedparser HTML sanitisation web site).
    151
    152      ``safe_attrs``:
    153          A set of attribute names to override the default list of attributes
    154          considered 'safe' (when safe_attrs_only=True).
    155
    156      ``add_nofollow``:
    157          If true, then any <a> tags will have ``rel="nofollow"`` added to them.
    158
    159      ``host_whitelist``:
    160          A list or set of hosts that you can use for embedded content
    161          (for content like ``<object>``, ``<link rel="stylesheet">``, etc).
    162          You can also implement/override the method
    163          ``allow_embedded_url(el, url)`` or ``allow_element(el)`` to
    164          implement more complex rules for what can be embedded.
    165          Anything that passes this test will be shown, regardless of
    166          the value of (for instance) ``embedded``.
    167
    168          Note that this parameter might not work as intended if you do not
    169          make the links absolute before doing the cleaning.
    170
    171          Note that you may also need to set ``whitelist_tags``.
    172
    173      ``whitelist_tags``:
    174          A set of tags that can be included with ``host_whitelist``.
    175          The default is ``iframe`` and ``embed``; you may wish to
    176          include other tags like ``script``, or you may want to
    177          implement ``allow_embedded_url`` for more control.  Set to None to
    178          include all tags.
    179
    180      This modifies the document *in place*.
    181      """
    182
    183      scripts = True
    184      javascript = True
    185      comments = True
    186      style = False
    187      links = True
    188      meta = True
    189      page_structure = True
    190      processing_instructions = True
    191      embedded = True
    192      frames = True
    193      forms = True
    194      annoying_tags = True
    195      remove_tags = None
    196      allow_tags = None
    197      kill_tags = None
    198      remove_unknown_tags = True
    199      safe_attrs_only = True
    200      safe_attrs = defs.safe_attrs
    201      add_nofollow = False
    202      host_whitelist = ()
    203      whitelist_tags = set(['iframe', 'embed'])
    204
    205 -    def __init__(self, **kw):
    206          for name, value in kw.items():
    207              if not hasattr(self, name):
    208                  raise TypeError(
    209                      "Unknown parameter: %s=%r" % (name, value))
    210              setattr(self, name, value)
    211
    212      # Used to lookup the primary URL for a given tag that is up for
    213      # removal:
    214      _tag_link_attrs = dict(
    215          script='src',
    216          link='href',
    217          # From: http://java.sun.com/j2se/1.4.2/docs/guide/misc/applet.html
    218          # From what I can tell, both attributes can contain a link:
    219          applet=['code', 'object'],
    220          iframe='src',
    221          embed='src',
    222          layer='src',
    223          # FIXME: there doesn't really seem like a general way to figure out what
    224          # links an <object> tag uses; links often go in <param> tags with values
    225          # that we don't really know.  You'd have to have knowledge about specific
    226          # kinds of plugins (probably keyed off classid), and match against those.
    227          ##object=?,
    228          # FIXME: not looking at the action currently, because it is more complex
    229          # than than -- if you keep the form, you should keep the form controls.
    230          ##form='action',
    231          a='href',
    232          )
    233
    234 -    def __call__(self, doc):
    235          """
    236          Cleans the document.
    237          """
    238          if hasattr(doc, 'getroot'):
    239              # ElementTree instance, instead of an element
    240              doc = doc.getroot()
    241          # convert XHTML to HTML
    242          xhtml_to_html(doc)
    243          # Normalize a case that IE treats <image> like <img>, and that
    244          # can confuse either this step or later steps.
    245          for el in doc.iter('image'):
    246              el.tag = 'img'
    247          if not self.comments:
    248              # Of course, if we were going to kill comments anyway, we don't
    249              # need to worry about this
    250              self.kill_conditional_comments(doc)
    251
    252          kill_tags = set(self.kill_tags or ())
    253          remove_tags = set(self.remove_tags or ())
    254          allow_tags = set(self.allow_tags or ())
    255
    256          if self.scripts:
    257              kill_tags.add('script')
    258          if self.safe_attrs_only:
    259              safe_attrs = set(self.safe_attrs)
    260              for el in doc.iter():
    261                  attrib = el.attrib
    262                  for aname in attrib.keys():
    263                      if aname not in safe_attrs:
    264                          del attrib[aname]
    265          if self.javascript:
    266              if not (self.safe_attrs_only and
    267                      self.safe_attrs == defs.safe_attrs):
    268                  # safe_attrs handles events attributes itself
    269                  for el in doc.iter():
    270                      attrib = el.attrib
    271                      for aname in attrib.keys():
    272                          if aname.startswith('on'):
    273                              del attrib[aname]
    274              doc.rewrite_links(self._remove_javascript_link,
    275                                resolve_base_href=False)
    276              if not self.style:
    277                  # If we're deleting style then we don't have to remove JS links
    278                  # from styles, otherwise...
    279                  for el in _find_styled_elements(doc):
    280                      old = el.get('style')
    281                      new = _css_javascript_re.sub('', old)
    282                      new = _css_import_re.sub('', new)
    283                      if self._has_sneaky_javascript(new):
    284                          # Something tricky is going on...
    285                          del el.attrib['style']
    286                      elif new != old:
    287                          el.set('style', new)
    288                  for el in list(doc.iter('style')):
    289                      if el.get('type', '').lower().strip() == 'text/javascript':
    290                          el.drop_tree()
    291                          continue
    292                      old = el.text or ''
    293                      new = _css_javascript_re.sub('', old)
    294                      # The imported CSS can do anything; we just can't allow:
    295                      new = _css_import_re.sub('', old)
    296                      if self._has_sneaky_javascript(new):
    297                          # Something tricky is going on...
    298                          el.text = '/* deleted */'
    299                      elif new != old:
    300                          el.text = new
    301          if self.comments or self.processing_instructions:
    302              # FIXME: why either?  I feel like there's some obscure reason
    303              # because you can put PIs in comments...?  But I've already
    304              # forgotten it
    305              kill_tags.add(etree.Comment)
    306          if self.processing_instructions:
    307              kill_tags.add(etree.ProcessingInstruction)
    308          if self.style:
    309              kill_tags.add('style')
    310              etree.strip_attributes(doc, 'style')
    311          if self.links:
    312              kill_tags.add('link')
    313          elif self.style or self.javascript:
    314              # We must get rid of included stylesheets if Javascript is not
    315              # allowed, as you can put Javascript in them
    316              for el in list(doc.iter('link')):
    317                  if 'stylesheet' in el.get('rel', '').lower():
    318                      # Note this kills alternate stylesheets as well
    319                      if not self.allow_element(el):
    320                          el.drop_tree()
    321          if self.meta:
    322              kill_tags.add('meta')
    323          if self.page_structure:
    324              remove_tags.update(('head', 'html', 'title'))
    325          if self.embedded:
    326              # FIXME: is <layer> really embedded?
    327              # We should get rid of any <param> tags not inside <applet>;
    328              # These are not really valid anyway.
    329              for el in list(doc.iter('param')):
    330                  found_parent = False
    331                  parent = el.getparent()
    332                  while parent is not None and parent.tag not in ('applet', 'object'):
    333                      parent = parent.getparent()
    334                  if parent is None:
    335                      el.drop_tree()
    336              kill_tags.update(('applet',))
    337              # The alternate contents that are in an iframe are a good fallback:
    338              remove_tags.update(('iframe', 'embed', 'layer', 'object', 'param'))
    339          if self.frames:
    340              # FIXME: ideally we should look at the frame links, but
    341              # generally frames don't mix properly with an HTML
    342              # fragment anyway.
    343              kill_tags.update(defs.frame_tags)
    344          if self.forms:
    345              remove_tags.add('form')
    346              kill_tags.update(('button', 'input', 'select', 'textarea'))
    347          if self.annoying_tags:
    348              remove_tags.update(('blink', 'marquee'))
    349
    350          _remove = []
    351          _kill = []
    352          for el in doc.iter():
    353              if el.tag in kill_tags:
    354                  if self.allow_element(el):
    355                      continue
    356                  _kill.append(el)
    357              elif el.tag in remove_tags:
    358                  if self.allow_element(el):
    359                      continue
    360                  _remove.append(el)
    361
    362          if _remove and _remove[0] == doc:
    363              # We have to drop the parent-most tag, which we can't
    364              # do.  Instead we'll rewrite it:
    365              el = _remove.pop(0)
    366              el.tag = 'div'
    367              el.attrib.clear()
    368          elif _kill and _kill[0] == doc:
    369              # We have to drop the parent-most element, which we can't
    370              # do.  Instead we'll clear it:
    371              el = _kill.pop(0)
    372              if el.tag != 'html':
    373                  el.tag = 'div'
    374              el.clear()
    375
    376          _kill.reverse() # start with innermost tags
    377          for el in _kill:
    378              el.drop_tree()
    379          for el in _remove:
    380              el.drop_tag()
    381
    382          if self.remove_unknown_tags:
    383              if allow_tags:
    384                  raise ValueError(
    385                      "It does not make sense to pass in both allow_tags and remove_unknown_tags")
    386              allow_tags = set(defs.tags)
    387          if allow_tags:
    388              bad = []
    389              for el in doc.iter():
    390                  if el.tag not in allow_tags:
    391                      bad.append(el)
    392              if bad:
    393                  if bad[0] is doc:
    394                      el = bad.pop(0)
    395                      el.tag = 'div'
    396                      el.attrib.clear()
    397                  for el in bad:
    398                      el.drop_tag()
    399          if self.add_nofollow:
    400              for el in _find_external_links(doc):
    401                  if not self.allow_follow(el):
    402                      rel = el.get('rel')
    403                      if rel:
    404                          if ('nofollow' in rel
    405                                  and ' nofollow ' in (' %s ' % rel)):
    406                              continue
    407                          rel = '%s nofollow' % rel
    408                      else:
    409                          rel = 'nofollow'
    410                      el.set('rel', rel)
    411
    412 -    def allow_follow(self, anchor):
    413          """
    414          Override to suppress rel="nofollow" on some anchors.
    415          """
    416          return False
    417
    418 -    def allow_element(self, el):
    419          if el.tag not in self._tag_link_attrs:
    420              return False
    421          attr = self._tag_link_attrs[el.tag]
    422          if isinstance(attr, (list, tuple)):
    423              for one_attr in attr:
    424                  url = el.get(one_attr)
    425                  if not url:
    426                      return False
    427                  if not self.allow_embedded_url(el, url):
    428                      return False
    429              return True
    430          else:
    431              url = el.get(attr)
    432              if not url:
    433                  return False
    434              return self.allow_embedded_url(el, url)
    435
    436 -    def allow_embedded_url(self, el, url):
    437          if (self.whitelist_tags is not None
    438              and el.tag not in self.whitelist_tags):
    439              return False
    440          scheme, netloc, path, query, fragment = urlsplit(url)
    441          netloc = netloc.lower().split(':', 1)[0]
    442          if scheme not in ('http', 'https'):
    443              return False
    444          if netloc in self.host_whitelist:
    445              return True
    446          return False
    447
    448 -    def kill_conditional_comments(self, doc):
    449          """
    450          IE conditional comments basically embed HTML that the parser
    451          doesn't normally see.  We can't allow anything like that, so
    452          we'll kill any comments that could be conditional.
    453          """
    454          bad = []
    455          self._kill_elements(
    456              doc, lambda el: _conditional_comment_re.search(el.text),
    457              etree.Comment)
    458
    459 -    def _kill_elements(self, doc, condition, iterate=None):
    460          bad = []
    461          for el in doc.iter(iterate):
    462              if condition(el):
    463                  bad.append(el)
    464          for el in bad:
    465              el.drop_tree()
    466
    467 -    def _remove_javascript_link(self, link):
    468          # links like "j a v a s c r i p t:" might be interpreted in IE
    469          new = _substitute_whitespace('', link)
    470          if _is_javascript_scheme(new):
    471              # FIXME: should this be None to delete?
    472              return ''
    473          return link
    474
    475      _substitute_comments = re.compile(r'/\*.*?\*/', re.S).sub
    476
    477 -    def _has_sneaky_javascript(self, style):
    478          """
    479          Depending on the browser, stuff like ``e x p r e s s i o n(...)``
    480          can get interpreted, or ``expre/* stuff */ssion(...)``.  This
    481          checks for attempt to do stuff like this.
    482
    483          Typically the response will be to kill the entire style; if you
    484          have just a bit of Javascript in the style another rule will catch
    485          that and remove only the Javascript from the style; this catches
    486          more sneaky attempts.
    487          """
    488          style = self._substitute_comments('', style)
    489          style = style.replace('\\', '')
    490          style = _substitute_whitespace('', style)
    491          style = style.lower()
    492          if 'javascript:' in style:
    493              return True
    494          if 'expression(' in style:
    495              return True
    496          return False
    497
    498 -    def clean_html(self, html):
    499          result_type = type(html)
    500          if isinstance(html, basestring):
    501              doc = fromstring(html)
    502          else:
    503              doc = copy.deepcopy(html)
    504          self(doc)
    505          return _transform_result(result_type, doc)
    506
    507  clean = Cleaner()
    508  clean_html = clean.clean_html
    509
    510  ############################################################
    511  ## Autolinking
    512  ############################################################
    513
    514  _link_regexes = [
    515      re.compile(r'(?P<body>https?://(?P<host>[a-z0-9._-]+)(?:/[/\-_.,a-z0-9%&?;=~]*)?(?:\([/\-_.,a-z0-9%&?;=~]*\))?)', re.I),
    516      # This is conservative, but autolinking can be a bit conservative:
    517      re.compile(r'mailto:(?P<body>[a-z0-9._-]+@(?P<host>[a-z0-9_._]+[a-z]))', re.I),
    518      ]
    519
    520  _avoid_elements = ['textarea', 'pre', 'code', 'head', 'select', 'a']
    521
    522  _avoid_hosts = [
    523      re.compile(r'^localhost', re.I),
    524      re.compile(r'\bexample\.(?:com|org|net)$', re.I),
    525      re.compile(r'^127\.0\.0\.1$'),
    526      ]
    527
    528  _avoid_classes = ['nolink']
    529
    530 -def autolink(el, link_regexes=_link_regexes,
    531               avoid_elements=_avoid_elements,
    532               avoid_hosts=_avoid_hosts,
    533               avoid_classes=_avoid_classes):
    534      """
    535      Turn any URLs into links.
    536
    537      It will search for links identified by the given regular
    538      expressions (by default mailto and http(s) links).
    539
    540      It won't link text in an element in avoid_elements, or an element
    541      with a class in avoid_classes.  It won't link to anything with a
    542      host that matches one of the regular expressions in avoid_hosts
    543      (default localhost and 127.0.0.1).
    544
    545      If you pass in an element, the element's tail will not be
    546      substituted, only the contents of the element.
    547      """
    548      if el.tag in avoid_elements:
    549          return
    550      class_name = el.get('class')
    551      if class_name:
    552          class_name = class_name.split()
    553          for match_class in avoid_classes:
    554              if match_class in class_name:
    555                  return
    556      for child in list(el):
    557          autolink(child, link_regexes=link_regexes,
    558                   avoid_elements=avoid_elements,
    559                   avoid_hosts=avoid_hosts,
    560                   avoid_classes=avoid_classes)
    561          if child.tail:
    562              text, tail_children = _link_text(
    563                  child.tail, link_regexes, avoid_hosts, factory=el.makeelement)
    564              if tail_children:
    565                  child.tail = text
    566                  index = el.index(child)
    567                  el[index+1:index+1] = tail_children
    568      if el.text:
    569          text, pre_children = _link_text(
    570              el.text, link_regexes, avoid_hosts, factory=el.makeelement)
    571          if pre_children:
    572              el.text = text
    573              el[:0] = pre_children
    574
    575 -def _link_text(text, link_regexes, avoid_hosts, factory):
    576      leading_text = ''
    577      links = []
    578      last_pos = 0
    579      while 1:
    580          best_match, best_pos = None, None
    581          for regex in link_regexes:
    582              regex_pos = last_pos
    583              while 1:
    584                  match = regex.search(text, pos=regex_pos)
    585                  if match is None:
    586                      break
    587                  host = match.group('host')
    588                  for host_regex in avoid_hosts:
    589                      if host_regex.search(host):
    590                          regex_pos = match.end()
    591                          break
    592                  else:
    593                      break
    594              if match is None:
    595                  continue
    596              if best_pos is None or match.start() < best_pos:
    597                  best_match = match
    598                  best_pos = match.start()
    599          if best_match is None:
    600              # No more matches
    601              if links:
    602                  assert not links[-1].tail
    603                  links[-1].tail = text
    604              else:
    605                  assert not leading_text
    606                  leading_text = text
    607              break
    608          link = best_match.group(0)
    609          end = best_match.end()
    610          if link.endswith('.') or link.endswith(','):
    611              # These punctuation marks shouldn't end a link
    612              end -= 1
    613              link = link[:-1]
    614          prev_text = text[:best_match.start()]
    615          if links:
    616              assert not links[-1].tail
    617              links[-1].tail = prev_text
    618          else:
    619              assert not leading_text
    620              leading_text = prev_text
    621          anchor = factory('a')
    622          anchor.set('href', link)
    623          body = best_match.group('body')
    624          if not body:
    625              body = link
    626          if body.endswith('.') or body.endswith(','):
    627              body = body[:-1]
    628          anchor.text = body
    629          links.append(anchor)
    630          text = text[end:]
    631      return leading_text, links
    632
    633 -def autolink_html(html, *args, **kw):
    634      result_type = type(html)
    635      if isinstance(html, basestring):
    636          doc = fromstring(html)
    637      else:
    638          doc = copy.deepcopy(html)
    639      autolink(doc, *args, **kw)
    640      return _transform_result(result_type, doc)
    641
    642  autolink_html.__doc__ = autolink.__doc__
    643
    644  ############################################################
    645  ## Word wrapping
    646  ############################################################
    647
    648  _avoid_word_break_elements = ['pre', 'textarea', 'code']
    649  _avoid_word_break_classes = ['nobreak']
    650
    651 -def word_break(el, max_width=40,
    652                 avoid_elements=_avoid_word_break_elements,
    653                 avoid_classes=_avoid_word_break_classes,
    654                 break_character=unichr(0x200b)):
    655      """
    656      Breaks any long words found in the body of the text (not attributes).
    657
    658      Doesn't effect any of the tags in avoid_elements, by default
    659      ``<textarea>`` and ``<pre>``
    660
    661      Breaks words by inserting &#8203;, which is a unicode character
    662      for Zero Width Space character.  This generally takes up no space
    663      in rendering, but does copy as a space, and in monospace contexts
    664      usually takes up space.
    665
    666      See http://www.cs.tut.fi/~jkorpela/html/nobr.html for a discussion
    667      """
    668      # Character suggestion of &#8203 comes from:
    669      #   http://www.cs.tut.fi/~jkorpela/html/nobr.html
    670      if el.tag in _avoid_word_break_elements:
    671          return
    672      class_name = el.get('class')
    673      if class_name:
    674          dont_break = False
    675          class_name = class_name.split()
    676          for avoid in avoid_classes:
    677              if avoid in class_name:
    678                  dont_break = True
    679                  break
    680          if dont_break:
    681              return
    682      if el.text:
    683          el.text = _break_text(el.text, max_width, break_character)
    684      for child in el:
    685          word_break(child, max_width=max_width,
    686                     avoid_elements=avoid_elements,
    687                     avoid_classes=avoid_classes,
    688                     break_character=break_character)
    689          if child.tail:
    690              child.tail = _break_text(child.tail, max_width, break_character)
    691
    692 -def word_break_html(html, *args, **kw):
    693      result_type = type(html)
    694      doc = fromstring(html)
    695      word_break(doc, *args, **kw)
    696      return _transform_result(result_type, doc)
    697
    698 -def _break_text(text, max_width, break_character):
    699      words = text.split()
    700      for word in words:
    701          if len(word) > max_width:
    702              replacement = _insert_break(word, max_width, break_character)
    703              text = text.replace(word, replacement)
    704      return text
    705
    706  _break_prefer_re = re.compile(r'[^a-z]', re.I)
    707
    708 -def _insert_break(word, width, break_character):
    709      orig_word = word
    710      result = ''
    711      while len(word) > width:
    712          start = word[:width]
    713          breaks = list(_break_prefer_re.finditer(start))
    714          if breaks:
    715              last_break = breaks[-1]
    716              # Only walk back up to 10 characters to find a nice break:
    717              if last_break.end() > width-10:
    718                  # FIXME: should the break character be at the end of the
    719                  # chunk, or the beginning of the next chunk?
    720                  start = word[:last_break.end()]
    721          result += start + break_character
    722          word = word[len(start):]
    723      result += word
    724      return result
    725