chore: Updating final Attributes docs for v3

markdown/dev/reference/api/attributes/renderifprefixis/en.md

@@ -0,0 +1,24 @@
+---
+title: Attributes.renderIfPrefixIs()
+---
+
+The `Attributes.renderIfPrefixIs()` method will render attributes as a string
+suitable for inclusion in an SVG tag, but only those attribute keys who start
+with `prefix`.
+
+## Signature
+
+```js
+string attributes.renderIfPrefixIs(string prefix)
+```
+
+## Example
+
+```js
+const attr = new Attributes()
+  .add('class', 'various')
+  .add('stroke', 'red')
+  .add('stroke-width', 2)
+
+const line = `<path ${attr.renderIfPrefixIs('stroke')} d="M 0,0 L 100.0" />`
+```