In reply to Chip Bennett.

Thank you, Chip! This is the kind of discussion of Post Formats, or other tech-'mysteries', that I like to see.

I'm not on my dev-platform right now, but can get a start on my response to Mr. Bennett's reply. I'd like to point to some additional specifics, a little later when I have my test-site up.

Chip Bennett authors the WordPress theme, Eonology. It is installed on my localhost site (with a few dozen others). Why Eonolgy?

[Eonology is] intended to serve as a base for child Themes and as an educational reference for Theme development using WordPress functions, action/filter hooks, and template tags. Oenology includes built-in breadcrumb navigation, and supports the Theme Customizer, Contextual Help, Post Formats, Navigation Menus, Post Thumbnails, Custom Backgrounds, Custom Image Headers, and Custom Editor Style. [emph. added]

Eonolgy is a learning-aid, and it does Post Formats. I had been using the 'official' Toolbox theme, as an educational tool ... but then it disappeared from the WordPress repository. I picked it for my main work-theme, in hopes that being produced by WordPress, it would be updated & stable.

While I understand "Post" as a record in a table in the database, I'm unclear what the Post Format innovation does (creates?) that is different. I will be on my dev-system this morning, and will look at the template files for Eonology, and prepare to track how WordPress knows that a given record/Post has been modified (?) to have a Post Format status.