Yes, these variables are called META variables. If you're on the IRC channel, you've probably heard me mention them quite a bit recently.

Two reasons:
1. Dancer does not use TT's WRAPPER functionality, since it doesn't exist everywhere (and definitely is not called the same, nor written the same, everywhere). Dancer does its own wrapper (called layout) for you. The downside is that you don't get TT's WRAPPER, but Dancer's layout. The upside is that every template engine (even Template::Tiny) gets a layout, which is awesome.
2. Since Dancer does not use TT's WRAPPER, you do not have META variables. META variables are created by TT's Finite State Machine (FSM) processing of the templates. It does not (as far as I know) allow you to separate these two states and provide the META variables separately. It *has* to go through TT's WRAPPER functionality and be done using TT's FSM engine.

Dancer is not using the WRAPPER, but provides its own called "layout". That's the summary.

But I have more! :)

Recently I've been contributing to the Dancer code of the PEG (Perl Ecosystem Group) website[1] and the one thing that *had* to be fixed was these META variables. There was a lot of content that should have been in templates but instead lay hardcoded inside the routes file. So I set about to fix it.

I've been able to get META variables working relatively easily. I wanted to write a post about it, but haven't gotten around to it yet. Here is a short explanation of how I did it:

1. In the configuration I removed the layout entry.
2. I added a configuration for the template engine and set up the layout as a WRAPPER:
engine:
  template_toolkit:
    WRAPPER: 'layouts/main.tt'

3. Now you can use META variables.

Here you can see the commit diff that accomplishes it:
https://github.com/xsawyerx/peg/commit/68876b226a9ff7aca4f222bc7e7aacdf99c539c8

[1] https://github.com/szabgab/peg