A list item can begin with at most one blank line.

[mity]

MD4C does not currently follow the rule of CommonMark spec 0.27 that

a list item can begin with at most one blank line.

Therefore we fail the Example 241.

However when we literally implement the rule as per this patch:

diff --git a/md4c/md4c.c b/md4c/md4c.c
index aae2a63..a82d458 100644
--- a/md4c/md4c.c
+++ b/md4c/md4c.c
@@ -4833,6 +4833,18 @@ redo:
             ctx->last_line_has_list_loosening_effect = (n_parents > 0  &&
                     n_brothers + n_children == 0  &&
                     ctx->containers[n_parents-1].ch != _T('>'));
+
+            /* If current list item contains nothing but a single blank line
+             * and we would be second blank line in the same list item, then
+             * we and the list. */
+            if(n_parents > 0  &&  ctx->containers[n_parents-1].ch != _T('>')  &&
+               n_brothers + n_children == 0  &&  ctx->current_block == NULL  &&
+               ctx->n_block_bytes > sizeof(MD_BLOCK))
+            {
+                MD_BLOCK* top_block = (MD_BLOCK*) ((char*)ctx->block_bytes + ctx->n_block_bytes - sizeof(MD_BLOCK));
+                if(top_block->type == MD_BLOCK_LI)
+                    n_parents--;
+            }
         }
         goto done;
     } else {

then we stop to pass the Example 274.

After inspecting, it looks as a contradiction in the spec to me. Fired the issue commonmark/commonmark-spec#443 for it.

[mity]

Fixed.

Somewhat hacky, as the rule is quite unnatural given our implementation design, but works.

At least we can celebrate passing complete CommonMark 0.27 test suite.
https://www.youtube.com/watch?v=Szdziw4tI9o