Remove leading newline in block attributes

src/Markdig.Tests/Specs/GenericAttributesSpecs.generated.cs

@@ -98,5 +98,22 @@ public void ExtensionsGenericAttributes_Example003()
 
             TestParser.TestSpec("[Foo](url){data-x=1}\n\n[Foo](url){data-x='1'}\n\n[Foo](url){data-x=11}", "<p><a href=\"url\" data-x=\"1\">Foo</a></p>\n<p><a href=\"url\" data-x=\"1\">Foo</a></p>\n<p><a href=\"url\" data-x=\"11\">Foo</a></p>", "attributes|advanced", context: "Example 3\nSection Extensions / Generic Attributes\n");
         }
+
+        // Attributes that occur immediately before a block element, on a line by themselves, affect that element
+        [Test]
+        public void ExtensionsGenericAttributes_Example004()
+        {
+            // Example 4
+            // Section: Extensions / Generic Attributes
+            //
+            // The following Markdown:
+            //     {.center}
+            //     A paragraph
+            //
+            // Should be rendered as:
+            //     <p class="center">A paragraph</p>
+
+            TestParser.TestSpec("{.center}\nA paragraph", "<p class=\"center\">A paragraph</p>", "attributes|advanced", context: "Example 4\nSection Extensions / Generic Attributes\n");
+        }
     }
 }

src/Markdig.Tests/Specs/GenericAttributesSpecs.md

@@ -61,3 +61,12 @@ Attribute values can be one character long
 <p><a href="url" data-x="1">Foo</a></p>
 <p><a href="url" data-x="11">Foo</a></p>
 ````````````````````````````````
+
+Attributes that occur immediately before a block element, on a line by themselves, affect that element
+
+```````````````````````````````` example
+{.center}
+A paragraph
+.
+<p class="center">A paragraph</p>
+````````````````````````````````

src/Markdig/Extensions/GenericAttributes/GenericAttributesParser.cs

@@ -109,6 +109,10 @@ public static bool TryParse(ref StringSlice slice, [NotNullWhen(true)] out HtmlA
             {
                 isValid = true;
                 line.SkipChar(); // skip }
+                if (line.CurrentChar == '\n')
+                {
+                    line.SkipChar(); // skip \n
+                }
                 break;
             }