Most of the time when I double tap a word in a reply on mobile, it highlights the word as I’d expect. Sometimes though, it just zooms in and out instead. I had this happen on another install, but they were way out of date so I wrote it off as an old bug that had already been fixed. However, I just had it happen here on meta a few minutes ago. After closing the tab and reopening it again though, it starting working again.
Can someone confirm that double tapping to highlight (instead of zoom) is the expected behavior? Has anyone seen this zoom issue before or have any insight into why this is happening? It’s hard to tell at this point if this is an intermittent bug or something else.
Why do that? Tap and hold works to select a word and avoids the awful desktop mouse paradigm of “double clicking”.
Also do you mean in an editor area or regular page text?
The editor. I thought using the word “reply” would make that clear but I see now that that term I still ambiguous. Sorry for the confusion.
I don’t know about other mobile operating systems and browsers, but in iOS safari the alternative to double tapping is actually tap and hold for about a second, then release, then tap the Select button. So double tapping is much faster.
Here’s a video from here on meta for reference. Every time the page jumps up or zooms in/out I’m double tapping to try to highlight a word.
I feel like anything other than tap-and-hold is intentionally swimming upstream. 
Double tapping in inputs/text areas to highlight on iOS seems to be the expected behavior everywhere. Double tapping results in highlighting the tapped word in messages, spotlight search, Safari search, renaming a folder, settings search, etc. Additionally, since we are talking about inputs on Safari, double tapping correctly highlights the tapped word on the websites Amazon, Facebook, and YouTube, just to name a few.
So this is an intermittent thing? I just don’t see double or triple or quad or penta tapping as a primary user activity. Especially since the simpler, and more mobile-centric “tap and hold” is available.
It is intermittent, though not that rare. Might happen once every day or two. Maybe a bit more. But sometimes closing the tab and reopening it doesn’t help, so maybe it’s from some kind of race condition on page load.
As I’ve stated before, this is much slower than double tapping. Besides, when double tap to highlight works everywhere else, it’s reasonable to get into the habit of doing so. Meaning that I’m going to try to do so out of habit on Discourse as well, which makes it that much more jarring when it doesn’t work as expected.