Steps to reproduce the problem
Create or edit a work
In the summary, type in some raw HTML specifying a class, e.g.: <p class="3foo">text</p>
Save the work, then either view the page source or edit it again to see the HTML in the summary field.
Notice that it still contains <p class="3foo">text</p> even though that isn't a valid CSS class
CSS classes starting with a digit, a hyphen, or containing non alphanumeric characters should be stripped out.
This should be as simple as adding :summary to the FIELDS_ALLOWING_CSS list in config.yml and then removing the corresponding skip in the html_cleaner_spec test.