Lower-case, markup and HTML entities removed, then everything but letters and
digits dropped — so a trailing period, a re-flowed line, <i> around a title
or an upper-cased DOI (doi.org content negotiation returns
10.25921/3W9F-JD72) is not drift. Author-name abbreviation IS drift, on
purpose: Keeling, C.D. and Keeling, Charles D. are different strings.