Currently, there's no useful way for the user (or the client, really) to know what is the "current" message is. This makes it hard to implement features that operate on individual messages, since it's not clear to the user which message the feature applies to.

As an example, we work around this when replying with selected text by looking for the message that last had some selected text, determining if it is visible, and if so making it a reply to that message. But that feels pretty hacky. Other examples are Ctrl+P to print (Bug 714908), saving messages (Bug 774023), and in general pretty much anything that could make use of a global shortcut.

After Bug 765516 landed a conversation is now displayed in a Gtk.ListBox, and I've tried using its different selection modes, but it confuses message expanding/collapsing with selection, and the highlighting used to indicate is completely over the top. It might still be usable, but some alternative method to handle expanding/contracting and highlight the selected message would be needed. It also needs to not conflict with the unread message indicator (currently a thick blue line at the top of the message).

So I'm thinking that the best option might be to make selecting messages an explicit action, i.e. to use Selection Mode: https://developer.gnome.org/hig/stable/selection-mode.html.en — in this case, invoking operations like Print without any selection would operate on the whole conversation, but if selection mode is enabled it only operates on the selected messages.

The hackyness replying to messages with selected text could then be handed by also making it an explicit action, per Bug 778724, which tidies everything up quite nicely.