docs: update style guide skill with prop naming conventions for boolean props

.github/skills/style-guide/SKILL.md

@@ -1,6 +1,6 @@
 ---
 name: style-guide
-description: 'Use when: authoring, modifying, or reviewing Primer React components, hooks, utilities, or component APIs. Covers applying contributor-docs/style.md, including the spectrum of abstraction, presentational components, behavior hooks, config components, accessibility primitives, props, hooks, SSR, and CSS conventions.'
+description: 'Use when: authoring, modifying, or reviewing Primer React components, hooks, utilities, or component APIs.'
 ---
 
 # Primer React Style Guide
@@ -16,3 +16,10 @@ repository.
 When proposing, implementing, or reviewing a component change, explicitly apply
 the relevant style-guide principles to the design. If a change intentionally
 deviates from the style guide, call out the reason.
+
+In addition, there are a set of topics below that may be used for guidance on a
+specific topic. Consult this to see if any apply to the task at hand.
+
+| Topic                 | Description                                                               | Link                                                     |
+| :-------------------- | :------------------------------------------------------------------------ | :------------------------------------------------------- |
+| Component prop naming | Use when deciding or evaluating the name for a prop in a React component. | [component-prop-naming](./docs/component-prop-naming.md) |

.github/skills/style-guide/docs/component-prop-naming.md

@@ -0,0 +1,143 @@
+# Component Prop Naming
+
+Use these conventions when creating, editing, or evaluating props for Primer React components.
+
+<!-- prettier-ignore-start -->
+<!-- START doctoc generated TOC please keep comment here to allow auto update -->
+<!-- DON'T EDIT THIS SECTION, INSTEAD RE-RUN doctoc TO UPDATE -->
+## Table of Contents
+
+- [Boolean props](#boolean-props)
+  - [Name state props as a bare adjective](#name-state-props-as-a-bare-adjective)
+  - [Prefix default values with `default*`](#prefix-default-values-with-default)
+  - [Name configuration props based on durable defaults](#name-configuration-props-based-on-durable-defaults)
+  - [Use `hide` or `show` for visibility-related props](#use-hide-or-show-for-visibility-related-props)
+  - [Prefer named modes for behavior with multiple options](#prefer-named-modes-for-behavior-with-multiple-options)
+  - [Use a single mode prop instead of mutually exclusive boolean props](#use-a-single-mode-prop-instead-of-mutually-exclusive-boolean-props)
+
+<!-- END doctoc generated TOC please keep comment here to allow auto update -->
+<!-- prettier-ignore-end -->
+
+## Boolean props
+
+### Name state props as a bare adjective
+
+Component props that represent state must be named without a prefix. For
+example:
+
+- Prefer `open` over `isOpen`
+- Prefer `expanded` over `isExpanded`
+- Prefer `selected` over `isSelected`
+
+### Prefix default values with `default*`
+
+When exposing a default value for a state prop, prefix the bare adjective with
+`default*`. For example:
+
+- Prefer `defaultOpen` over `defaultIsOpen`
+- Prefer `defaultExpanded` over `defaultIsExpanded`
+- Prefer `defaultSelected` over `defaultIsSelected`
+
+### Name configuration props based on durable defaults
+
+When a prop is used to configure what a component does, for example hiding a
+title, name the prop after the non-default action a consumer takes. For example:
+
+- Use `hideTitle` when the title is visible by default
+- Use `showDivider` when the divider is hidden by default
+- Use `hideCloseButton` when the close button is visible by default
+
+This helps avoid inverted naming. For example, a prop named `showTitle` may end up
+being passed as `false` in most usage, whereas a prop named `hideTitle` would
+typically be passed as `true`.
+
+A default is durable when:
+
+- It is part of the component's structural contract, such as whether an optional
+  part is rendered
+- It is consistent across variants, viewport sizes, and usage contexts
+- Changing it would be an intentional design change rather than an implementation
+  detail or contextual adjustment
+- The non-default action has a concise, unambiguous name
+
+If a default varies by context or both values represent meaningful behaviors,
+prefer a stable state name or named modes. The prop name should continue to
+describe the requested behavior if the default changes. For example:
+
+```tsx
+// Avoid
+type ExampleProps = {
+  disableTruncation?: boolean
+  disableStickyPositioning?: boolean
+}
+
+// Prefer
+type ExampleProps = {
+  textOverflow?: 'truncate' | 'wrap'
+  position?: 'sticky' | 'static'
+}
+```
+
+### Use `hide` or `show` for visibility-related props
+
+When a configuration prop adds or removes a named optional part of a component
+and has one stable default, use `hide` or `show` in the prop name. For example:
+
+- Use `hideTitle` when the title is visible by default
+- Use `showDivider` when the divider is hidden by default
+
+For visibility state, native HTML semantics, or responsive values, names such as
+`hidden` may be appropriate.
+
+### Prefer named modes for behavior with multiple options
+
+When behavior has multiple meaningful modes, prefer a named string-literal union
+that describes those modes. For example:
+
+```tsx
+// Avoid
+type ExampleProps = {
+  preventOverflow?: boolean
+}
+
+// Prefer
+type ExampleProps = {
+  overflow?: 'auto' | 'prevent'
+}
+```
+
+Keep a boolean prop for a stable binary capability or state, such as `disabled`,
+`required`, or `loading`, or for configuration based on a durable default. Use a
+discriminated union when a mode determines which other props are valid. For
+example:
+
+```tsx
+type ExampleProps =
+  | {
+      variant: 'icon'
+      'aria-label': string
+    }
+  | {
+      variant: 'text'
+      children: React.ReactNode
+    }
+```
+
+### Use a single mode prop instead of mutually exclusive boolean props
+
+When a component has multiple boolean props that are mutually exclusive, replace
+them with one string-literal union prop. This makes it clear that only one option
+can be selected at a time and improves type safety. For example:
+
+```tsx
+// Avoid
+type ExampleProps = {
+  singleSelect?: boolean
+  multiSelect?: boolean
+}
+
+// Prefer
+type ExampleProps = {
+  selectionVariant?: 'single' | 'multiple'
+}
+```