I've taken the time to review most of the documentation and familiarize myself with the forward-facing Backdrop interface. Let me just say that I love it; having been a long-time Drupal 7 user I truly love the direction this CMS is going.
That said, I'm very confused on the theme/layout relationship.
For example: If I make a page and I only want that one page to have a script, I would make a custom html.tpl.php template page for that situation so I could put my script in the head. When I look through all the theme files and layout files, I can't figure out how the HTML is being generated. Where is the body tag? Where is the head tag? Where is opening and closing html tags? Where are these things to be found?
(You might want to consider a "How It Works" section in the documentation: The layout files do X. The theme files do Y. The final output is Z. How do we combine X and Y together to get Z?)
I can't figure it out from what I've read. Maybe somebody can help me get past this stumbling block. I can't start a new project. I want to make a sub-theme (seems the safest way to get started). What should I make it off of (I did see that documentation). All the stuff that I expect to see in a Drupal 7 template section I don't see. How has that process changed?
I need a shove in the right direction - thanks.