Where are placeholders defined?

Where are the placeholders I can use in triggers etc. defined? I don’t have any Ruby experience so following the code is proving a little difficult so a shove in the right direction would help.
I need a way to show the previous article as well as the newest when sending an email to the customer after a reply from an agent. That way the customer can see what was last said to refresh their memory. Having access to all articles would be great for that too.
I’ve seen feature requests for similar but haven’t seen anything come out of it so I figured if I could see where this magic happens I could start piecing my own solution together.

Are you looking for email quoting as a regular email client would do? As in, all the previous replies are copied below your response? As described here: Original e-mail inclusion at the bottom of sent e-mails · Issue #571 · zammad/zammad · GitHub

This is possible as of version 2.0.0. The setting for it is a little hidden. At the top of any ticket, hit the gear and you will see a few options. One will look like this:

Let me know if you still can’t find it. Happy to help. I just set up Zammad and went thru this myself.

I’m also now trying to see if I can get the sender, date, etc. above the full quote (Email - full quote time specification · Issue #1426 · zammad/zammad · GitHub)… perhaps you would like to help with that if you get a chance and also find it useful?