Fix primitive values

index.js

@@ -66,14 +66,16 @@ function element(node, schema) {
   function h(name, attrs) {
     var values = []
     var p5
+    var attr
     var value
     var key
     var info
     var pos
 
     for (key in attrs) {
       info = find(schema, key)
-      value = {name: key, value: attrs[key]}
+      attr = attrs[key]
+      value = {name: key, value: attr === true ? '' : String(attr)}
 
       if (info.space && ignoredSpaces.indexOf(info.space) === -1) {
         pos = key.indexOf(':')

test/element.js

@@ -21,6 +21,81 @@ test('element', function(t) {
     st.end()
   })
 
+  t.test('should transform attributes', function(st) {
+    var actual = toParse5({
+      type: 'element',
+      tagName: 'div',
+      properties: {},
+      children: [
+        {
+          type: 'element',
+          tagName: 'h1',
+          properties: {id: 'a', className: ['b', 'c'], hidden: true, height: 2},
+          children: [
+            {type: 'text', value: 'alpha '},
+            {
+              type: 'element',
+              tagName: 'strong',
+              properties: {
+                style: 'color:red;',
+                // Unknown booleans are ignored.
+                ignored: false,
+                // Falsey known booleans are ignored.
+                disabled: 0,
+                // Unknown props are left as-is.
+                foo: 'bar',
+                // Unknown lists are space-separated.
+                // Note: you’d expect `camelCase` here, but p5 lowercases
+                // attributes on HTML, so it drops the camelcase.
+                camelcase: ['on', 'off'],
+                // Numeric-start data properties.
+                data123: '456',
+                // Data properties.
+                dataSome: 'yes',
+                // ARIA props.
+                ariaValuenow: '1'
+              },
+              children: [{type: 'text', value: 'bravo'}]
+            },
+            {type: 'text', value: ' charlie'}
+          ]
+        },
+        {
+          type: 'element',
+          tagName: 'input',
+          properties: {
+            checked: true,
+            type: 'file',
+            // Known comma-separated lists:
+            accept: ['.jpg', '.jpeg']
+          },
+          children: []
+        }
+      ]
+    })
+
+    var expected = parse5.parseFragment(
+      [
+        '<div>',
+        '<h1 id="a" class="b c" hidden height="2">',
+        'alpha ',
+        '<strong style="color:red;" foo="bar" camelCase="on off" data-123="456" data-some="yes" aria-valuenow="1">',
+        'bravo',
+        '</strong>',
+        ' charlie',
+        '</h1>',
+        '<input checked type="file" accept=".jpg, .jpeg">',
+        '</div>'
+      ].join('')
+    ).childNodes[0]
+
+    delete expected.parentNode
+
+    st.deepEqual(json(actual), json(expected))
+
+    st.end()
+  })
+
   t.test('should transform void elements', function(st) {
     var actual = toParse5({
       type: 'element',