It doesn’t seem to, though I could be mistaken.

  1. the “browser” (viewer or renderer in this case) has to support the feature. For example, Chrome still doesn’t fully support this feature, whereas Firefox has for some time (Firefox is usually a bit ahead of everyone else in maturity).
  2. The language has to be properly set. This is usually done in the tag, which we can’t, as users, define. If I searched it out correctly, this is how the top of the viewer rendered html is declared:
<!DOCTYPE html>
<html>
<head id="joplin-container-root-head">
	<meta charset="UTF-8">

If I found the correct HTML from Joplin, that <html> tag is empty, and ideally it should not be. The <html ... > should have it’s lang attribute set. For me that would be "en" (see below). For others it would be something else. The challenge is that language could change note to note. Technically, it could change within the note, and the folks that need that sort of thing need to figure it out for themselves (see my <div ... > example further on. You’d likely want a default language (set in options), but then some mechanism to change it per note in Joplin. That would be the pedantic ideal. I’m not sure how far we’d want to take this, but the language setting should be set to something and right now it is set to nothing.

<html lang="en" xml:lang="en" xmlns="http://www.w3.org/1999/xhtml">

So. Two RFEs. Well, one is arguably a bug.

  1. BUG: Your language setting in the Joplin Options should set the default lang attribute in the viewer’s html.
  2. RFE: Make sure the hyphens css property works (it doesn’t, see below).

To test #2, I did this at the top of my markdown document …

<style type="text/css">
p, li {
  /* It almost looks like the Joplin viewer doesn't support any of these */
  word-wrap: break-word;
  overflow-wrap: break-word;
  hyphens: auto;
}
p {
  text-align: justify;
  text-justify: auto;
}
li, li p {
  text-align: left;
}
</style>
<div lang="en" xml:lang="en" xmlns="http://www.w3.org/1999/xhtml" style="width: 6.5in;">

The content of my document starts here. Blah blah. Big long article.

</div>

And no hyphenation occurs.