fix: constructed-stylesheet shadow runs and missing type declarations

README.md

@@ -61,7 +61,7 @@ been applied.
 ### Constructed stylesheets (`adoptedStyleSheets`)
 
 If your custom elements use [constructed stylesheets](https://developer.mozilla.org/en-US/docs/Web/API/CSSStyleSheet/CSSStyleSheet)
-(via `new CSSStyleSheet()` + `replaceSync()` + `shadowRoot.adoptedStyleSheets`), call `patchAndPolyfillConstructedStylesheets()` **before** any custom element's `connectedCallback` runs:
+(via `new CSSStyleSheet()` + `replaceSync()` + `shadowRoot.adoptedStyleSheets`), call `patchAndPolyfillConstructedStylesheets()` **before** any of those custom elements are defined:
 
 ```html
 <script type="module">
@@ -83,10 +83,27 @@ import { patchAndPolyfillConstructedStylesheets } from '@oddbird/css-anchor-posi
 patchAndPolyfillConstructedStylesheets();
 ```
 
-This patches `CSSStyleSheet.prototype.replaceSync` to capture
-stylesheet source text, and patches the `ShadowRoot.prototype.adoptedStyleSheets`
-setter to automatically run the polyfill for each shadow root once its host
-element's `connectedCallback` finishes.
+This patches `CSSStyleSheet.prototype.replaceSync` to capture stylesheet source
+text, and patches the `ShadowRoot.prototype.adoptedStyleSheets` setter to
+automatically run the polyfill for each shadow root, deferred until its host is
+connected and its shadow DOM has been populated.
+
+A host that adopts its stylesheet _before_ it is connected is positioned only if
+it is a custom element defined after
+`patchAndPolyfillConstructedStylesheets()` is called.
+
+Those automatic runs use the same [options](#configuration) as `polyfill()`,
+either passed directly or read from
+`window.ANCHOR_POSITIONING_POLYFILL_OPTIONS`:
+
+```js
+patchAndPolyfillConstructedStylesheets({ positionAreaContainingBlock: false });
+```
+
+The `roots` and `elements` options are ignored, since each run is scoped to the
+shadow root being positioned. The global is read when each run happens, not when
+`patchAndPolyfillConstructedStylesheets()` is called, so it can still be set
+afterwards; an explicit argument takes precedence over the global.
 
 You can view a more complete demo
 [here](https://anchor-positioning.oddbird.net/shadow-dom.html).