Fix some props

Closes rehypejs/rehype#127.

lib/index.js

@@ -61,6 +61,9 @@ import {location} from 'vfile-location'
 import {webNamespaces} from 'web-namespaces'
 
 const own = {}.hasOwnProperty
+/** @type {unknown} */
+// type-coverage:ignore-next-line
+const proto = Object.prototype
 
 /**
  * Transform a `parse5` AST to hast.
@@ -215,8 +218,11 @@ function element(state, node) {
 
   while (++index < node.attrs.length) {
     const attribute = node.attrs[index]
-    props[(attribute.prefix ? attribute.prefix + ':' : '') + attribute.name] =
-      attribute.value
+    const name =
+      (attribute.prefix ? attribute.prefix + ':' : '') + attribute.name
+    if (!own.call(proto, name)) {
+      props[name] = attribute.value
+    }
   }
 
   // Build.

test/index.js

@@ -355,6 +355,18 @@ test('fromParse5', () => {
     },
     'should transform svg'
   )
+
+  assert.deepEqual(
+    fromParse5(parseFragment('<x constructor y />'), {space: 'svg'}),
+    {
+      type: 'root',
+      children: [
+        {type: 'element', tagName: 'x', properties: {y: ''}, children: []}
+      ],
+      data: {quirksMode: false}
+    },
+    'should ignore prototypal props'
+  )
 })
 
 test('fixtures', async () => {