Joomla field capabilities:

• scans configured folders with PHP layouts;
• shows available options in a dropdown, including template overrides (/templates/{template}/html/...);
• saves the selected value into field rawvalue with layout and basePath (JSON);
• provides computed value in value (layout_id) that can be used with Joomla LayoutHelper::render().

This field is useful when you want to let a content manager choose a layout variant without editing template PHP files:
- articles (comcontent): article sections, cards, CTA blocks;
- contacts (comcontact): different contact card templates;
- categories and lists: different partial layouts for different contexts;
- module output zones: include content/modules in the required layout variant.
- ability to create reusable layout blocks for Joomla landing pages.