This seems like it would be easier to read as a multiline string:
```python
# at the top of the file
import cgi

# code I'm commenting on
if self.system.DEBUG:
    msg = """
<html>
  <div class="inline-error">
    <p>Error {err}</p>
    <p>Failed to construct targeted feedback from <pre>{html}</pre></p>
  </div>
</html>
    """.format(err=cgi.escape(err), html=cgi.escape(html)
    log.err(msg)
    return etree.XML(msg)
```