* `<af-field>` should reference legit fields.
* Future consideration: how to validate when it's part of a subform?
* `<af-fieldset>` should reference a declared model.
-* `<af-field field-defn="...">` should contain an object.
+* `<af-field defn="...">` should contain an object.
* `<a>` should have `href` or `ng-click` or `af-api4-action`
* Accept a restricted subset of HTML (e.g. `p h1 h2 h3` but not `script` or `[onclick]`)
* Accept a restricted subset of BootstrapCSS