Recently I started using PHP Markdown Extra in order to format my posts. I decided to make the switch mostly because I find writing Markdown slightly more natural than writing HTML; more than that though I find reading and editing posts I’ve previously written using Markdown to be as easy as reading a regular word document or a book. Of course, the readability of Markdown text was sort of the point of the syntax so my observations seem a touch obvious. The crux of my point stems from my reasons for switching so it felt necessary to elucidate my position.

Through the course of learning the Markdown Extra Syntax I found it supported footnotes, for me this was exciting because I have a tendency when writing to have a lot of tangential thoughts. I usually¹ use parentheticals to capture these ancillary musings but I have noticed this tends to detract from the primary issue during reading. Clarity is something I strive for when writing² and so I figured it would be better to store my tangents away from the rest where they wouldn’t detract from the point I was trying to get across.³

I jumped into using footnotes with both feet and had soon written two posts⁴ making liberal use of footnotes. Upon inspection of the posts on the front page I noticed the references didn’t behave correctly. After some brief investigation I discovered the ids were the same for every set of footnotes which was frustrating for a couple reasons.

1. The footnotes aren’t much use if they don’t actually work
2. Duplicate ids means the document won’t validate, which makes me sad.

I immediately descended on the problem in an attempt to rectify the situation. To make a long⁵ story short I ended up creating a SHA1 hash of the footnote’s text and using it as an identifier for the references and ids. This works quite well for my purposes since it seems fairly unlikely I’ll be using the same footnote text over and over again⁶, however there are some pretty obvsious weaknesses to this strategy, which I’ll outline below. But first I wanted to provide a downloadable patch of the changes I made in order to make this footnote stuff work: you can get the Wordpress Friendly Markdown Footnotes patch and apply it in order to get this working for yourself. I created the patch using git, so if it proves difficult to apply let me know in the comments or via one of the contact methods on my about page and I’ll fix it up lickity split.

Now about those weaknesses; the major problem comes about if you want to use the same footnote text a couple of times. I could see this coming about more on a site publishing research papers than here but that isn’t the point. A better method would have been to use the Wordpress post id via <?php the_ID(); ?> because then the footnote references for the post are all constrained by a shared value. This was in fact my first idea but it seems core Wordpress loop functions are not available inside filters. This made me wonder if perhaps there wasn’t another way to get the post id, either from a filter argument or from some other magical place. Needless to say I couldn’t figure another way out or I would have used the post id method instead. Another issue, though I guess it’s not really a weakness, is the SHA1 makes the references a bit long and unsightly, not to mention meaningless. However, I was just happy to get the thing to work.

That is all for now, I’ll post updates if I make any improvments or changes.