Also use it for pages

Author: FlorianRappl

src/AngleSharp.Css/Dom/Internal/Rules/CssPageRule.cs

@@ -45,6 +45,11 @@ public String SelectorText
 
         #region Methods
 
+        internal void SetInvalidSelector(String selectorText)
+        {
+            _selector = new InvalidSelector(selectorText);
+        }
+
         protected override void ReplaceWith(ICssRule rule)
         {
             var newRule = (ICssPageRule)rule;
@@ -59,5 +64,29 @@ public override void ToCss(TextWriter writer, IStyleFormatter formatter)
         }
 
         #endregion
+
+        #region Selector
+
+        class InvalidSelector : ISelector
+        {
+            private readonly String _text;
+
+            public InvalidSelector(String text)
+            {
+                _text = text;
+            }
+
+            public String Text => _text;
+
+            public Priority Specificity => Priority.Zero;
+
+            public void Accept(ISelectorVisitor visitor)
+            {
+            }
+
+            public Boolean Match(IElement element, IElement scope) => false;
+        }
+
+        #endregion
     }
 }

src/AngleSharp.Css/Parser/CssBuilder.cs

@@ -271,7 +271,15 @@ private CssNamespaceRule CreateNamespace(CssNamespaceRule rule, CssToken current
         private CssPageRule CreatePage(CssPageRule rule, CssToken current)
         {
             current = NextToken();
-            rule.SelectorText = GetArgument(ref current);
+            var selectorText = GetArgument(ref current);
+
+            rule.SelectorText = selectorText;
+
+            if (rule.Selector is null && _options.IsToleratingInvalidSelectors)
+            {
+                rule.SetInvalidSelector(selectorText);
+            }
+            
             CollectTrivia(ref current);
 
             if (current.Type != CssTokenType.CurlyBracketOpen)