# Block parts and site block types

Source: [Block parts and site block types](https://typeroll.com/docs/tools/blocks/parts/)

> Style the parts of built-in and site block types, and how site block types behave in the editor, API and publication.

Part of the [block reference](https://typeroll.com/docs/tools/blocks/). Changes by Core release are listed in [Block changes by Core version](https://typeroll.com/docs/tools/blocks/changelog/).

## Site block types

When the library doesn’t fit, an editor or site administrator builds a block type for the site: composed from existing blocks (recommended) or with its own markup, with editable fields, repeating groups and scoped CSS. See [Site block types](https://typeroll.com/docs/tools/custom-block-types/).

Caution

**Block JavaScript runs in every visitor’s browser.** Through MCP and the API, `create_block_type` and `update_block_type` accept a `script` field, and `core/embed` accepts `js`, under your API key’s authority — the same content-authoring permission. This is also available to editors through personal OAuth and in the portal’s block-type editor (“Activate JS”). The write is stored as sent and recorded in the API audit log like any other change. Review scripts like deployed code, and never paste script you copied from untrusted content without reading it first. A `<script>` tag in page or block markup is still removed by the sanitizer, whichever credential wrote it.

The in-portal chat assistant is the one exception: it writes block JavaScript only when the site has **Allow AI to write block scripts** enabled. A site admin sets that in **Settings → Custom code**, or with `update_site` (`ai_scripts_enabled: true`) / `PATCH /api/v1/sites/{siteId}`. The setting has no effect on API keys or MCP.

Core blocks (id starts with `core/`) are managed in platform code and can’t be changed. A block type in use cannot be deleted; `find_pages_using_block_type` lists where it is used.

## Block parts

A **part** is a named element inside a block that a [named style](https://typeroll.com/docs/tools/styles/) can style: the links in a formatted heading, a hero’s heading or buttons. It replaces CSS against the block’s markup (`[data-block="rich_heading"] a`) with a style the editor shows, that follows the site’s palette and is checked for contrast. `read_block_type` returns a type’s `parts`:

```json
{
  "id": "core/rich_heading",
  "parts": [
    { "name": "link", "label": "Links", "selector": "a", "target": "link" }
  ]
}
```

Each part has a `target`, the kind of style that fits it (`text`, `heading`, `list`, `button`, `container`, `link` or `image`); only styles that can be chosen for that kind apply.

### Parts of the core blocks

| Block                                             | Part                | Element                                      | Style kind | Chosen per block with |
| ------------------------------------------------- | ------------------- | -------------------------------------------- | ---------- | --------------------- |
| Accordion (`core/accordion`)                      | `item`              | Item (render v4)                             | container  | `part_styles`         |
|                                                   | `title`             | Item title (render v4)                       | text       | `part_styles`         |
|                                                   | `panel`             | Item content (render v4)                     | text       | `part_styles`         |
| Breadcrumbs (`template/page_breadcrumbs`)         | `item`              | Items                                        | text       | `part_styles`         |
|                                                   | `link`              | Links                                        | link       | `part_styles`         |
|                                                   | `current`           | Current page                                 | text       | `part_styles`         |
| Button (`core/button`)                            | `link`              | Button                                       | button     | `style_id`            |
| Checkbox group (`form/checkbox_group`)            | `label`             | Label                                        | text       | `part_styles`         |
|                                                   | `choice`            | Choice row                                   | container  | `part_styles`         |
|                                                   | `choice_mark`       | Choice mark                                  | container  | `part_styles`         |
|                                                   | `choice_label`      | Choice text                                  | text       | `part_styles`         |
|                                                   | `help`              | Help text                                    | text       | `part_styles`         |
|                                                   | `error`             | Error message                                | text       | `part_styles`         |
| Consent checkbox (`form/consent`)                 | `choice`            | Checkbox row                                 | container  | `part_styles`         |
|                                                   | `choice_mark`       | Checkbox                                     | container  | `part_styles`         |
|                                                   | `text`              | Consent text                                 | text       | `part_styles`         |
|                                                   | `link`              | Links                                        | link       | `part_styles`         |
|                                                   | `error`             | Error message                                | text       | `part_styles`         |
| CTA (`core/cta`)                                  | `eyebrow`           | Eyebrow                                      | text       | `part_styles`         |
|                                                   | `heading`           | Heading                                      | heading    | `part_styles`         |
|                                                   | `subheading`        | Subheading                                   | text       | `part_styles`         |
|                                                   | `primary_button`    | Primary button                               | button     | `part_styles`         |
|                                                   | `secondary_button`  | Secondary button                             | button     | `part_styles`         |
|                                                   | `actions`           | Button row                                   | container  | `part_styles`         |
| Date field (`form/date`)                          | `label`             | Label                                        | text       | `part_styles`         |
|                                                   | `input`             | Input                                        | container  | `part_styles`         |
|                                                   | `help`              | Help text                                    | text       | `part_styles`         |
|                                                   | `error`             | Error message                                | text       | `part_styles`         |
| Email field (`form/email`)                        | `label`             | Label                                        | text       | `part_styles`         |
|                                                   | `input`             | Input                                        | container  | `part_styles`         |
|                                                   | `help`              | Help text                                    | text       | `part_styles`         |
|                                                   | `error`             | Error message                                | text       | `part_styles`         |
| Expandable help (`form/help`)                     | `summary`           | Question                                     | text       | `part_styles`         |
|                                                   | `body`              | Help content                                 | text       | `part_styles`         |
|                                                   | `link`              | Links                                        | link       | `part_styles`         |
| Feature row (`core/feature_row`)                  | `eyebrow`           | Eyebrow                                      | text       | `part_styles`         |
|                                                   | `heading`           | Heading                                      | heading    | `part_styles`         |
|                                                   | `text`              | Text                                         | text       | `part_styles`         |
|                                                   | `primary_button`    | Primary button                               | button     | `part_styles`         |
|                                                   | `secondary_button`  | Secondary button                             | button     | `part_styles`         |
|                                                   | `media`             | Image                                        | image      | `part_styles`         |
|                                                   | `layout`            | Image and text columns                       | container  | `part_styles`         |
|                                                   | `actions`           | Button row                                   | container  | `part_styles`         |
| Form section heading (`form/heading`)             | `heading`           | Heading                                      | heading    | `part_styles`         |
|                                                   | `description`       | Intro line                                   | text       | `part_styles`         |
| Formatted heading (`core/rich_heading`)           | `link`              | Links                                        | link       | `part_styles`         |
| Heading (`core/heading`)                          | `eyebrow`           | Eyebrow                                      | text       | `eyebrow_style_id`    |
|                                                   | `text`              | Heading                                      | heading    | `style_id`            |
|                                                   | `subtitle`          | Subtitle (render v2)                         | text       | `subtitle_style_id`   |
| Hero (`core/hero`)                                | `eyebrow`           | Eyebrow                                      | text       | `part_styles`         |
|                                                   | `heading`           | Heading                                      | heading    | `part_styles`         |
|                                                   | `subheading`        | Subheading                                   | text       | `part_styles`         |
|                                                   | `primary_button`    | Primary button                               | button     | `part_styles`         |
|                                                   | `secondary_button`  | Secondary button                             | button     | `part_styles`         |
|                                                   | `media`             | Image                                        | image      | `part_styles`         |
|                                                   | `layout`            | Text and image columns                       | container  | `part_styles`         |
|                                                   | `actions`           | Button row                                   | container  | `part_styles`         |
|                                                   | `overlay`           | Image overlay                                | container  | `part_styles`         |
| Icon Box (`core/icon_box`)                        | `icon`              | Icon                                         | container  | `part_styles`         |
|                                                   | `heading`           | Heading                                      | heading    | `part_styles`         |
|                                                   | `text`              | Body text                                    | text       | `part_styles`         |
|                                                   | `link`              | Link                                         | link       | `part_styles`         |
| Image (`core/image`)                              | `frame`             | Image frame                                  | image      | `part_styles`         |
|                                                   | `image`             | Image                                        | image      | `part_styles`         |
|                                                   | `caption`           | Caption                                      | text       | `part_styles`         |
|                                                   | `caption_link`      | Caption links                                | link       | `part_styles`         |
| List (`core/list`)                                | `list`              | List                                         | list       | `part_styles`         |
|                                                   | `item`              | Items                                        | text       | `part_styles`         |
|                                                   | `link`              | Links                                        | link       | `part_styles`         |
| Logo (`core/logo_item`)                           | `logo`              | Logo image                                   | image      | `part_styles`         |
| Media card (`core/media_card`)                    | `body`              | Text column                                  | container  | `part_styles`         |
|                                                   | `heading`           | Heading                                      | heading    | `part_styles`         |
|                                                   | `text`              | Text                                         | text       | `part_styles`         |
|                                                   | `button`            | Button                                       | button     | `part_styles`         |
|                                                   | `media`             | Image                                        | image      | `part_styles`         |
| Navigation (`core/navigation`)                    | `list`              | Link list                                    | list       | `part_styles`         |
|                                                   | `link`              | Links                                        | link       | `part_styles`         |
|                                                   | `current_link`      | Current page link                            | link       | `part_styles`         |
|                                                   | `toggle`            | Menu button                                  | button     | `part_styles`         |
| Navigation inputs (`core/navigation_form`)        | `field`             | Field                                        | container  | `part_styles`         |
|                                                   | `label`             | Labels                                       | text       | `part_styles`         |
|                                                   | `input`             | Inputs                                       | container  | `part_styles`         |
|                                                   | `button`            | Button                                       | button     | `part_styles`         |
|                                                   | `button_icon`       | Button icon                                  | text       | `part_styles`         |
| Navigation links (`core/navigation_links`)        | `link`              | Links                                        | link       | `part_styles`         |
|                                                   | `current_link`      | Link to the current page                     | link       | `part_styles`         |
|                                                   | `icon`              | Link icons                                   | text       | `part_styles`         |
| Number field (`form/number`)                      | `label`             | Label                                        | text       | `part_styles`         |
|                                                   | `input`             | Input                                        | container  | `part_styles`         |
|                                                   | `help`              | Help text                                    | text       | `part_styles`         |
|                                                   | `error`             | Error message                                | text       | `part_styles`         |
| Page author (`template/page_author`)              | `avatar`            | Avatar                                       | image      | `part_styles`         |
|                                                   | `prefix`            | Prefix                                       | text       | `part_styles`         |
|                                                   | `name`              | Author name                                  | text       | `part_styles`         |
| Page field list (`core/field_list`)               | `title`             | Heading                                      | heading    | `part_styles`         |
|                                                   | `list`              | Field list                                   | list       | `part_styles`         |
|                                                   | `row`               | Row                                          | container  | `part_styles`         |
|                                                   | `label`             | Field label                                  | text       | `part_styles`         |
|                                                   | `value`             | Field value                                  | text       | `part_styles`         |
|                                                   | `values`            | Value list                                   | list       | `part_styles`         |
|                                                   | `link`              | Links                                        | link       | `part_styles`         |
| Phone field (`form/phone`)                        | `label`             | Label                                        | text       | `part_styles`         |
|                                                   | `input`             | Input                                        | container  | `part_styles`         |
|                                                   | `help`              | Help text                                    | text       | `part_styles`         |
|                                                   | `error`             | Error message                                | text       | `part_styles`         |
| Post Card (`core/post_card`)                      | `image`             | Image or placeholder                         | image      | `part_styles`         |
|                                                   | `image_link`        | Image link                                   | link       | `part_styles`         |
|                                                   | `placeholder_icon`  | Placeholder icon                             | text       | `part_styles`         |
|                                                   | `title`             | Title                                        | heading    | `part_styles`         |
|                                                   | `title_link`        | Title link                                   | link       | `part_styles`         |
|                                                   | `title_icon`        | Title icon                                   | text       | `part_styles`         |
|                                                   | `excerpt`           | Excerpt                                      | text       | `part_styles`         |
|                                                   | `meta`              | Date and author                              | text       | `part_styles`         |
|                                                   | `action`            | Page action link                             | link       | `part_styles`         |
|                                                   | `download`          | Download link                                | link       | `part_styles`         |
| Previous / next page (`template/page_navigation`) | `previous_link`     | Previous link                                | button     | `part_styles`         |
|                                                   | `next_link`         | Next link                                    | button     | `part_styles`         |
|                                                   | `label`             | Previous and Next labels                     | text       | `part_styles`         |
|                                                   | `title`             | Page titles                                  | text       | `part_styles`         |
| Pricing Plan (`core/pricing_plan`)                | `badge`             | Badge                                        | text       | `part_styles`         |
|                                                   | `name`              | Plan name                                    | heading    | `part_styles`         |
|                                                   | `price`             | Price                                        | text       | `part_styles`         |
|                                                   | `period`            | Period                                       | text       | `part_styles`         |
|                                                   | `description`       | Tagline                                      | text       | `part_styles`         |
|                                                   | `features`          | Feature list                                 | list       | `part_styles`         |
|                                                   | `included_feature`  | Included feature (render v4)                 | text       | `part_styles`         |
|                                                   | `excluded_feature`  | Excluded feature (render v4)                 | text       | `part_styles`         |
|                                                   | `button`            | Button                                       | button     | `part_styles`         |
| Radio group (`form/radio_group`)                  | `label`             | Label                                        | text       | `part_styles`         |
|                                                   | `choice`            | Choice row                                   | container  | `part_styles`         |
|                                                   | `choice_mark`       | Choice mark                                  | container  | `part_styles`         |
|                                                   | `choice_label`      | Choice text                                  | text       | `part_styles`         |
|                                                   | `help`              | Help text                                    | text       | `part_styles`         |
|                                                   | `error`             | Error message                                | text       | `part_styles`         |
| Repeater (`core/repeater`)                        | `carousel_controls` | Carousel controls (render v7)                | container  | `part_styles`         |
|                                                   | `carousel_button`   | Carousel arrow and pause buttons (render v7) | button     | `part_styles`         |
|                                                   | `carousel_dot`      | Carousel dots (render v7)                    | button     | `part_styles`         |
| Search (`core/search`)                            | `input`             | Search field                                 | text       | `part_styles`         |
|                                                   | `message`           | Result count                                 | text       | `part_styles`         |
|                                                   | `result_link`       | Result titles                                | link       | `part_styles`         |
|                                                   | `result_excerpt`    | Result excerpts                              | text       | `part_styles`         |
|                                                   | `more_button`       | More results button                          | button     | `part_styles`         |
|                                                   | `note`              | Unavailable note                             | text       | `part_styles`         |
| Select (`form/select`)                            | `label`             | Label                                        | text       | `part_styles`         |
|                                                   | `input`             | Input                                        | container  | `part_styles`         |
|                                                   | `help`              | Help text                                    | text       | `part_styles`         |
|                                                   | `error`             | Error message                                | text       | `part_styles`         |
| Site logo (`template/site_logo`)                  | `logo`              | Logo image                                   | image      | `part_styles`         |
| Slider (`form/slider`)                            | `label`             | Label                                        | text       | `part_styles`         |
|                                                   | `value`             | Value                                        | text       | `part_styles`         |
|                                                   | `help`              | Help text                                    | text       | `part_styles`         |
|                                                   | `error`             | Error message                                | text       | `part_styles`         |
| Step Card (`core/step_card`)                      | `marker`            | Number and icon row                          | container  | `part_styles`         |
|                                                   | `number`            | Step number                                  | text       | `part_styles`         |
|                                                   | `icon`              | Icon                                         | text       | `part_styles`         |
|                                                   | `title`             | Title                                        | heading    | `part_styles`         |
|                                                   | `text`              | Description                                  | text       | `part_styles`         |
| Table (`core/table`)                              | `table`             | Table                                        | container  | `part_styles`         |
|                                                   | `caption`           | Caption                                      | text       | `part_styles`         |
|                                                   | `header_cell`       | Header cells                                 | text       | `part_styles`         |
|                                                   | `cell`              | Cells                                        | text       | `part_styles`         |
|                                                   | `even_row`          | Even rows (stripes)                          | container  | `part_styles`         |
|                                                   | `link`              | Links                                        | link       | `part_styles`         |
|                                                   | `source`            | Source / credit                              | text       | `part_styles`         |
| Table of contents (`core/table_of_contents`)      | `title`             | Title                                        | text       | `part_styles`         |
|                                                   | `list`              | List                                         | list       | `part_styles`         |
|                                                   | `item`              | Item                                         | text       | `part_styles`         |
|                                                   | `link`              | Links                                        | link       | `part_styles`         |
|                                                   | `current_link`      | Current link                                 | link       | `part_styles`         |
| Tabs and links (`core/tabs`)                      | `headline`          | Inline headline                              | text       | `part_styles`         |
|                                                   | `strip`             | Choice row                                   | container  | `part_styles`         |
|                                                   | `choice`            | Tabs and links                               | button     | `part_styles`         |
|                                                   | `choice_icon`       | Choice icons                                 | text       | `part_styles`         |
|                                                   | `toggle`            | Open/close button                            | button     | `part_styles`         |
|                                                   | `panel`             | Panels                                       | container  | `part_styles`         |
| Team Member (`core/team_member`)                  | `card`              | Card                                         | container  | `part_styles`         |
|                                                   | `photo`             | Photo                                        | image      | `part_styles`         |
|                                                   | `body`              | Text panel                                   | container  | `part_styles`         |
|                                                   | `name`              | Name                                         | heading    | `part_styles`         |
|                                                   | `role`              | Role                                         | text       | `part_styles`         |
|                                                   | `bio`               | Bio                                          | text       | `part_styles`         |
|                                                   | `socials`           | Social links list                            | list       | `part_styles`         |
|                                                   | `social_link`       | Social link (render v4)                      | link       | `part_styles`         |
| Testimonial (`core/testimonial`)                  | `quote`             | Quote                                        | text       | `part_styles`         |
|                                                   | `rating`            | Rating (render v7)                           | text       | `part_styles`         |
|                                                   | `attribution`       | Attribution row                              | text       | `part_styles`         |
|                                                   | `avatar`            | Avatar                                       | image      | `part_styles`         |
|                                                   | `name`              | Name                                         | text       | `part_styles`         |
|                                                   | `role`              | Role and company                             | text       | `part_styles`         |
|                                                   | `logo`              | Company logo                                 | image      | `part_styles`         |
| Text (`core/prose`)                               | `heading_1`         | Heading 1                                    | heading    | `part_styles`         |
|                                                   | `heading_2`         | Heading 2                                    | heading    | `part_styles`         |
|                                                   | `heading_3`         | Heading 3                                    | heading    | `part_styles`         |
|                                                   | `heading_4`         | Heading 4                                    | heading    | `part_styles`         |
|                                                   | `link`              | Links                                        | link       | `part_styles`         |
|                                                   | `list`              | Lists                                        | list       | `part_styles`         |
|                                                   | `list_item`         | List items                                   | text       | `part_styles`         |
|                                                   | `quote`             | Quotes                                       | text       | `part_styles`         |
|                                                   | `code`              | Inline code                                  | text       | `part_styles`         |
|                                                   | `code_block`        | Code blocks                                  | text       | `part_styles`         |
|                                                   | `table_header`      | Table header cells                           | text       | `part_styles`         |
|                                                   | `table_cell`        | Table cells                                  | text       | `part_styles`         |
|                                                   | `image`             | Images                                       | image      | `part_styles`         |
| Text area (`form/textarea`)                       | `label`             | Label                                        | text       | `part_styles`         |
|                                                   | `input`             | Input                                        | container  | `part_styles`         |
|                                                   | `help`              | Help text                                    | text       | `part_styles`         |
|                                                   | `error`             | Error message                                | text       | `part_styles`         |
| Text field (`form/text`)                          | `label`             | Label                                        | text       | `part_styles`         |
|                                                   | `input`             | Input                                        | container  | `part_styles`         |
|                                                   | `help`              | Help text                                    | text       | `part_styles`         |
|                                                   | `error`             | Error message                                | text       | `part_styles`         |
| Toggle (`form/toggle`)                            | `choice`            | Toggle row                                   | container  | `part_styles`         |
|                                                   | `track`             | Switch                                       | container  | `part_styles`         |
|                                                   | `label`             | Label                                        | text       | `part_styles`         |
|                                                   | `help`              | Help text                                    | text       | `part_styles`         |
|                                                   | `error`             | Error message                                | text       | `part_styles`         |
| Two columns (`core/columns`)                      | `left_column`       | Left column                                  | container  | `part_styles`         |
|                                                   | `right_column`      | Right column                                 | container  | `part_styles`         |
| URL field (`form/url`)                            | `label`             | Label                                        | text       | `part_styles`         |
|                                                   | `input`             | Input                                        | container  | `part_styles`         |
|                                                   | `help`              | Help text                                    | text       | `part_styles`         |
|                                                   | `error`             | Error message                                | text       | `part_styles`         |
| Video (`core/video`)                              | `player`            | Player                                       | image      | `part_styles`         |
|                                                   | `facade`            | Video placeholder (click-to-load)            | button     | `part_styles`         |
|                                                   | `facade_label`      | Load video label                             | button     | `part_styles`         |
| Yes / No answer (`form/boolean`)                  | `label`             | Label                                        | text       | `part_styles`         |
|                                                   | `choice`            | Answer row                                   | container  | `part_styles`         |
|                                                   | `choice_mark`       | Answer mark                                  | container  | `part_styles`         |
|                                                   | `clear_button`      | Clear answer button                          | button     | `part_styles`         |
|                                                   | `help`              | Help text                                    | text       | `part_styles`         |
|                                                   | `error`             | Error message                                | text       | `part_styles`         |

Every core block with presentational CSS of its own declares its parts, and `read_block_type` lists them. Where a block already had a style field for an element (a heading’s eyebrow, a button’s link, a card’s surface through `style_id`), that field chooses the part’s style on one block. This table is checked against the block definitions in the test suite.

### Choose a style for a part on one block

In the editor: select the block, then **Appearance → Part styles**. Through MCP or the API: the block’s `part_styles` data, a map from part name to style id. Every block type with a part that has no style field of its own gets this field automatically.

```plaintext
update_block page_id=… block_id=… data={ part_styles: { heading: "hero-title", primary_button: "button-pill" } }
```

Like other object fields, `update_block` replaces the whole map rather than merging it, so send every part you want to keep; `null` removes the map. A chosen style replaces the site-wide style for that part on this block.

`add_block` and `update_block` refuse a write with `400`, writing nothing, when:

| Code                    | When                                                                                                                                                                                                                                                                                                 |
| ----------------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| `unknown_field`         | The block has no such part, or the part has its own style field. The path is `data.part_styles.<part>`, and the suggestions name the closest parts or the field to use (`eyebrow_style_id`). See [Unknown data fields](https://typeroll.com/docs/tools/blocks/parts/#unknown-data-fields-core-0279). |
| `unknown_style`         | The site has no style with that id. `suggestions` lists styles of the part’s kind.                                                                                                                                                                                                                   |
| `style_target_mismatch` | The style cannot be chosen for the part’s kind. `suggestions` lists styles that can.                                                                                                                                                                                                                 |
| `part_style_contrast`   | The style’s text fails both APCA and WCAG 2 AA on the part’s background.                                                                                                                                                                                                                             |

The style issues are listed in `part_style_issues`, each with its `path`, `part` and `style_id`. A value that is not a style id at all is a `field_type_mismatch` warning, and a contrast that misses only its APCA level a `part_style_contrast` warning. Page, partial and batch writes, which carry a whole tree, store the tree and return all of these as `warnings`.

The background a part is measured on is the block’s own background colour where it has one (a hero’s `background`), else the colour the block paints behind the part (the primary colour behind a primary button), else the site background. Layout parts and the overlay hold no text and are not measured.

### Apply a style to a part on every block

A style’s `parts` (**Block parts** in the style editor) lists parts as `<block type>.<part>`, and the style then applies to that part of every block of the type:

```plaintext
update_style style_id="quiet-link" targets=["link"] parts=["core/rich_heading.link"]
```

A part takes one site-wide style, and the style’s `targets` must include the part’s kind. A reference the site’s block types do not have is refused with the closest names. Precedence, from lowest: the block’s own look and fields, the default role style, the part style (the block’s `part_styles` choice, else the site-wide one), and a style class on the element itself (a heading’s `eyebrow_style_id`, a button’s `style_id`). See [Style parts of a block](https://typeroll.com/docs/tools/styles/#style-parts-of-a-block).

Part styles change nothing on a site that does not set one: the published markup and CSS stay the same, and no render version is involved.

### Parts on site block types

A [site block type](https://typeroll.com/docs/tools/custom-block-types/) declares its own parts in `parts` with `create_block_type` or `update_block_type` (which replaces the list):

```json
{
  "name": "price_card",
  "label": "Price card",
  "schema": [
    { "name": "title", "type": "text", "label": "Title" },
    { "name": "price", "type": "text", "label": "Price" }
  ],
  "template": "<div class=\"price-card\"><h3 class=\"price-card-title\">{{title}}</h3><p class=\"price-card-price\">{{price}}</p></div>",
  "parts": [
    {
      "name": "title",
      "label": "Title",
      "selector": ".price-card-title",
      "target": "heading"
    },
    {
      "name": "price",
      "label": "Price",
      "selector": ".price-card-price",
      "target": "text",
      "background": "surface"
    }
  ]
}
```

| Property             | Meaning                                                                                                                                                                              |
| -------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |
| `name`               | `a-z`, `0-9` and `_`, up to 32 characters, starting with a letter; unique in the type. Do not rename a part in use: `part_styles` and styles refer to it.                            |
| `label`              | Shown in the editor.                                                                                                                                                                 |
| `selector`           | The part’s element(s) relative to the block: tags, classes, attributes, structural pseudo-classes (`:first-child`, `:nth-child(2)`) and combinators, up to four separated by commas. |
| `target`             | The kind of style that fits: `text`, `heading`, `list`, `button`, `container`, `link` or `image`.                                                                                    |
| `style_field`        | A `style` field of the type that already chooses the part’s style on each block. `part_styles` then leaves the part out.                                                             |
| `color`              | The colour token of the part’s text in the block’s CSS, for contrast checks. Default `text`.                                                                                         |
| `background`         | The colour token behind the part, for contrast checks. Default the site background.                                                                                                  |
| `background_field`   | A `color` field of the type that holds the background behind the part.                                                                                                               |
| `decorative`         | `true` for a part without text of its own (an overlay, a layout row): its style is not checked for contrast.                                                                         |
| `min_render_version` | The render version from which the element exists.                                                                                                                                    |

Selectors may not contain braces, `;`, `@`, comments, pseudo-elements (`::before`) or state pseudo-classes such as `:hover` and `:focus`: hover comes from the style. A selector that starts with `>` selects a child of the block element (`> .gallery-item`); in a block that holds other blocks, anchor every part that way so it never reaches into a nested block. Where two parts overlap (all links, and the link to the current page), the part listed later wins. A type has at most 16 parts. A selector class that the template never writes is reported as a warning, because the part would match nothing. The type gets the `part_styles` field automatically when a part has no `style_field`, so do not declare a field of that name yourself. Parts are for template types; a composed type’s inner blocks keep their own parts.