LibMarkdown: Implement introspection of the document tree

Author: https://github.com/BenWiederhake
Commit: 24e7196158
Pull-request: https://github.com/SerenityOS/serenity/pull/10420
Reviewed-by: https://github.com/petelliott ✅

Userland/Libraries/LibMarkdown/BlockQuote.cpp

@@ -6,6 +6,7 @@
 
 #include <AK/StringBuilder.h>
 #include <LibMarkdown/BlockQuote.h>
+#include <LibMarkdown/Visitor.h>
 
 namespace Markdown {
 
@@ -24,6 +25,15 @@ String BlockQuote::render_for_terminal(size_t view_width) const
     return m_contents->render_for_terminal(view_width);
 }
 
+RecursionDecision BlockQuote::walk(Visitor& visitor) const
+{
+    RecursionDecision rd = visitor.visit(*this);
+    if (rd != RecursionDecision::Recurse)
+        return rd;
+
+    return m_contents->walk(visitor);
+}
+
 OwnPtr<BlockQuote> BlockQuote::parse(LineIterator& lines)
 {
     lines.push_context(LineIterator::Context::block_quote());