docs: def thumbnails(html):
      """
      Given a HTML string, converts paths in img tags to thumbnail
      paths, using yacms's ``thumbnail`` template tag. Used as
      one of the default values in the ``RICHTEXT_FILTERS`` setting.
      """
      from django.conf import settings
      from bs4 import BeautifulSoup
      from yacms.core.templatetags.yacms_tags import thumbnail
  
      # If MEDIA_URL isn't in the HTML string, there aren't any
      # images to replace, so bail early.
      if settings.MEDIA_URL.lower() not in html.lower():
          return html
  
      dom = BeautifulSoup(html, "html.parser")
      for img in dom.findAll("img"):
          src = img.get("src", "")
          src_in_media = src.lower().startswith(settings.MEDIA_URL.lower())
          width = img.get("width")
          height = img.get("height")
          if src_in_media and width and height:
              img["src"] = settings.MEDIA_URL + thumbnail(src, width, height)
      # BS adds closing br tags, which the browser interprets as br tags.
      return str(dom).replace("</br>", "")