Validation thoughts

description.md

If the value != null assertion fails in the leaf component, want the validation root to produce an error object that looks like

{
  "leaf": {
    "inner": {
      "required": true
    }
  }
}

leaf-component.html

<div validationPath="inner"
     [validations]="{required: value != null}"></div>

parent.html

<div validationRoot #root="validation">
  <leaf-component validationPath="leaf">
  </leaf-component>
  <button [disabled]="!root.valid"></button>
</div>