Thanks to a conversation on micro.blog I have changed the way I enter the <details>
tag.
There is custom markup for adding spoiler text on Stack Exchange, all you need to do is precede the text with the two characters > ! (but together) so I thought this would be a good place to start for details markup.
I've settled on this:
The filter looks for the text between the delimiters and surrounds it in the required <details><summary>
tags instead. I was previously entering the text on two lines with two sets of delimiters so this is more streamlined.
I've since found out that Reddit also uses similar syntax for hidden text so I'm in good company.