The < symbol does not show in notifications and can even hide text after it. It does get rendered properly in apps, so it seems to just be an issue in Plasma. I’m not too sure if its a misconfiguration on my part or a bug yet, so I decided not to report it.
Can confirm. Apparently this is because you can use some HTML tags like <b> or <a> to format text in notification bodies and invalid XML tags that are never closed throw it off.
You can actually get a ‘<’ character to display by using < in the notification, just like you would in HTML.
Glancing over the notification spec they do mention the markup formatting but I don’t see anything specifically about needing to escape / encode HTML special chars so I guess this could be considered a bug?
P. S. One can easily test this using the notify-send command like this:
notify-send "Title" "<b>bold</b> <i>italic</i> 1 < 2 and 2 < 3!"
(The Bold and italic text is rendered but the text is cut off at <)
It seems like it doesn’t sanitize the <script> html tag either, that might be a problem.
It’s not a full HTML renderer and definitely doesn’t execute Javascript as far as I can tell, that’s not an issue. It just happens to remove any XML tags it doesn’t know including the contained text.