XML builder: custom components, platform blocks, and its errors

Custom components

Point an xmlns prefix at a module path (relative to app/), then use exported view classes as tags:

<Page xmlns:ui="components/rating">
  <StackLayout>
    <ui:Rating value="3" />
  </StackLayout>
</Page>

• The module's exported symbol name is the tag (export class Rating extends GridLayout).
• A component folder can be XML-first: components/card/Card.xml (+ optional co-located Card.css, code-behind, or a package.json naming the entry) — usable with no JS class at all.
• Framework modules work through the same mechanism: xmlns:c="ui/label" → <c:Label>.
• Unknown attributes on a custom component become plain expando properties (panel['myProperty'] = 'myValue') — never an error, so attribute typos fail silently. Property names are checked nowhere; test bindings visually.
• Dashed lowercase tags are first-class: <stack-layout>, <segmented-bar> — and CSS type selectors must use that dashed form.