Development themes, nested blocks and custom field filters
Multiple development themes and a store theme API for the CLI
You can now keep more than one development theme per store. The development-theme panel under Online Store lists every one of them with its name, where it came from and when it last changed; pick which one you are editing with "Make current", preview any of them on your real storefront, publish one, or archive one you no longer need. The newest three archived development themes stay restorable. Theme developers get a store theme API for the MicroCart CLI: with an API key that has the new "store themes" permissions it can create a development theme on a store, upload files to it (every file is checked with Flow Check before it is saved), fetch a preview link and archive it again — publishing stays a click in the admin.
Nested theme blocks in the editor
The page outline in the theme editor now shows blocks inside blocks, up to eight levels deep, for themes that are built with theme blocks. Open and close a block with the arrow next to it or with the arrow keys, add a block inside another block from its own "Add block" row (including ready-made combinations the theme offers), drag blocks within a block or into another block of the same kind, and give any block your own name. Blocks the theme places in a fixed position are marked: you can change their settings and hide them, but not move or remove them. A section holds at most 50 blocks, and the editor tells you when you reach that. Your current theme works exactly as before.
Metafields can be used as storefront filters
A product custom field can now be offered as a filter in your storefront. Open Settings → Custom fields, edit a product field that holds one text, number, yes/no or colour value and is visible on the storefront, and tick "Use as a storefront filter". Themes built for the new theme format then show it as a collection and search filter with product counts, next to filters for your variant options such as size and colour.