Period at end of abbreviations

[nwtn]

(I'll have a PR for this momentarily, but I wanted to document the issue.)

If you have a period at the end of an abbreviation definition, the abbreviation is not replaced in the text. E.g.

Ph.D.

*[Ph.D.]: Doctor of Philosophy

…will produce <p>Ph.D.</p>, not <p><abbr title="Doctor of Philosophy">Ph.D.</abbr></p>.

Omitting the period from the abbreviation definition works, but then the final period in the text is not wrapped in the abbr element:

Ph.D.

*[Ph.D]: Doctor of Philosophy

…will produce <p><abbr title="Doctor of Philosophy">Ph.D</abbr>.</p>.