diff --git a/Makefile b/Makefile
index b92c1c11..9e682c56 100644
--- a/Makefile
+++ b/Makefile
@@ -21,6 +21,3 @@ ext/commonmarker/cmark-gfm_export.h: ext/commonmarker/cmark-upstream/build/src/c
 
 ext/commonmarker/cmark-gfm_version.h: ext/commonmarker/cmark-upstream/build/src/cmark-gfm_version.h
 	cp $< $@
-
-ext/commonmarker/cmark-gfm-extensions_export.h: ext/commonmarker/cmark-upstream/build/extensions/cmark-gfm-extensions_export.h
-	cp $< $@
diff --git a/ext/commonmarker/arena.c b/ext/commonmarker/arena.c
index 6373c0d0..da1a70e9 100644
--- a/ext/commonmarker/arena.c
+++ b/ext/commonmarker/arena.c
@@ -99,6 +99,6 @@ static void arena_free(void *ptr) {
 
 cmark_mem CMARK_ARENA_MEM_ALLOCATOR = {arena_calloc, arena_realloc, arena_free};
 
-cmark_mem *cmark_get_arena_mem_allocator() {
+cmark_mem *cmark_get_arena_mem_allocator(void) {
   return &CMARK_ARENA_MEM_ALLOCATOR;
 }
diff --git a/ext/commonmarker/autolink.c b/ext/commonmarker/autolink.c
index f3b75a7e..491d96c3 100644
--- a/ext/commonmarker/autolink.c
+++ b/ext/commonmarker/autolink.c
@@ -267,6 +267,11 @@ static cmark_node *url_match(cmark_parser *parser, cmark_node *parent,
   cmark_node *text = cmark_node_new_with_mem(CMARK_NODE_TEXT, parser->mem);
   text->as.literal = url;
   cmark_node_append_child(node, text);
+  
+  node->start_line = text->start_line = node->end_line = text->end_line = cmark_inline_parser_get_line(inline_parser);
+
+  node->start_column = text->start_column = max_rewind - rewind;
+  node->end_column = text->end_column = cmark_inline_parser_get_column(inline_parser) - 1;
 
   return node;
 }
diff --git a/ext/commonmarker/blocks.c b/ext/commonmarker/blocks.c
index 94045aba..03a58748 100644
--- a/ext/commonmarker/blocks.c
+++ b/ext/commonmarker/blocks.c
@@ -27,6 +27,14 @@
 #define CODE_INDENT 4
 #define TAB_STOP 4
 
+/**
+ * Very deeply nested lists can cause quadratic performance issues.
+ * This constant is used in open_new_blocks() to limit the nesting
+ * depth. It is unlikely that a non-contrived markdown document will
+ * be nested this deeply.
+ */
+#define MAX_LIST_DEPTH 100
+
 #ifndef MIN
 #define MIN(x, y) ((x < y) ? x : y)
 #endif
@@ -1119,10 +1127,11 @@ static void open_new_blocks(cmark_parser *parser, cmark_node **container,
   bool has_content;
   int save_offset;
   int save_column;
+  size_t depth = 0;
 
   while (cont_type != CMARK_NODE_CODE_BLOCK &&
          cont_type != CMARK_NODE_HTML_BLOCK) {
-
+    depth++;
     S_find_first_nonspace(parser, input);
     indented = parser->indent >= CODE_INDENT;
 
@@ -1224,6 +1233,7 @@ static void open_new_blocks(cmark_parser *parser, cmark_node **container,
       (*container)->internal_offset = matched;
     } else if ((!indented || cont_type == CMARK_NODE_LIST) &&
 	       parser->indent < 4 &&
+               depth < MAX_LIST_DEPTH &&
                (matched = parse_list_marker(
                     parser->mem, input, parser->first_nonspace,
                     (*container)->type == CMARK_NODE_PARAGRAPH, &data))) {
diff --git a/ext/commonmarker/cmark-gfm-core-extensions.h b/ext/commonmarker/cmark-gfm-core-extensions.h
index 0645915f..bc29ffd4 100644
--- a/ext/commonmarker/cmark-gfm-core-extensions.h
+++ b/ext/commonmarker/cmark-gfm-core-extensions.h
@@ -6,45 +6,45 @@ extern "C" {
 #endif
 
 #include "cmark-gfm-extension_api.h"
-#include "cmark-gfm-extensions_export.h"
-#include "config.h" // for bool
+#include "cmark-gfm_export.h"
+#include <stdbool.h>
 #include <stdint.h>
 
-CMARK_GFM_EXTENSIONS_EXPORT
+CMARK_GFM_EXPORT
 void cmark_gfm_core_extensions_ensure_registered(void);
 
-CMARK_GFM_EXTENSIONS_EXPORT
+CMARK_GFM_EXPORT
 uint16_t cmark_gfm_extensions_get_table_columns(cmark_node *node);
 
 /** Sets the number of columns for the table, returning 1 on success and 0 on error.
  */
-CMARK_GFM_EXTENSIONS_EXPORT
+CMARK_GFM_EXPORT
 int cmark_gfm_extensions_set_table_columns(cmark_node *node, uint16_t n_columns);
 
-CMARK_GFM_EXTENSIONS_EXPORT
+CMARK_GFM_EXPORT
 uint8_t *cmark_gfm_extensions_get_table_alignments(cmark_node *node);
 
 /** Sets the alignments for the table, returning 1 on success and 0 on error.
  */
-CMARK_GFM_EXTENSIONS_EXPORT
+CMARK_GFM_EXPORT
 int cmark_gfm_extensions_set_table_alignments(cmark_node *node, uint16_t ncols, uint8_t *alignments);
 
-CMARK_GFM_EXTENSIONS_EXPORT
+CMARK_GFM_EXPORT
 int cmark_gfm_extensions_get_table_row_is_header(cmark_node *node);
 
 /** Sets whether the node is a table header row, returning 1 on success and 0 on error.
  */
-CMARK_GFM_EXTENSIONS_EXPORT
+CMARK_GFM_EXPORT
 int cmark_gfm_extensions_set_table_row_is_header(cmark_node *node, int is_header);
 
-CMARK_GFM_EXTENSIONS_EXPORT
+CMARK_GFM_EXPORT
 bool cmark_gfm_extensions_get_tasklist_item_checked(cmark_node *node);
 /* For backwards compatibility */
 #define cmark_gfm_extensions_tasklist_is_checked cmark_gfm_extensions_get_tasklist_item_checked
 
 /** Sets whether a tasklist item is "checked" (completed), returning 1 on success and 0 on error.
  */
-CMARK_GFM_EXTENSIONS_EXPORT
+CMARK_GFM_EXPORT
 int cmark_gfm_extensions_set_tasklist_item_checked(cmark_node *node, bool is_checked);
 
 #ifdef __cplusplus
diff --git a/ext/commonmarker/cmark-gfm.h b/ext/commonmarker/cmark-gfm.h
index 6fb28693..0544057a 100644
--- a/ext/commonmarker/cmark-gfm.h
+++ b/ext/commonmarker/cmark-gfm.h
@@ -111,13 +111,13 @@ typedef struct cmark_mem {
  * realloc and free.
  */
 CMARK_GFM_EXPORT
-cmark_mem *cmark_get_default_mem_allocator();
+cmark_mem *cmark_get_default_mem_allocator(void);
 
 /** An arena allocator; uses system calloc to allocate large
  * slabs of memory.  Memory in these slabs is not reused at all.
  */
 CMARK_GFM_EXPORT
-cmark_mem *cmark_get_arena_mem_allocator();
+cmark_mem *cmark_get_arena_mem_allocator(void);
 
 /** Resets the arena allocator, quickly returning all used memory
  * to the operating system.
@@ -225,6 +225,11 @@ CMARK_GFM_EXPORT cmark_node *cmark_node_first_child(cmark_node *node);
  */
 CMARK_GFM_EXPORT cmark_node *cmark_node_last_child(cmark_node *node);
 
+/** Returns the footnote reference of 'node', or NULL if 'node' doesn't have a
+ * footnote reference.
+ */
+CMARK_GFM_EXPORT cmark_node *cmark_node_parent_footnote_def(cmark_node *node);
+
 /**
  * ## Iterator
  *
@@ -408,6 +413,17 @@ CMARK_GFM_EXPORT int cmark_node_get_list_tight(cmark_node *node);
  */
 CMARK_GFM_EXPORT int cmark_node_set_list_tight(cmark_node *node, int tight);
 
+/**
+ * Returns item index of 'node'. This is only used when rendering output
+ * formats such as commonmark, which need to output the index. It is not
+ * required for formats such as html or latex.
+ */
+CMARK_GFM_EXPORT int cmark_node_get_item_index(cmark_node *node);
+
+/** Sets item index of 'node'. Returns 1 on success, 0 on failure.
+ */
+CMARK_GFM_EXPORT int cmark_node_set_item_index(cmark_node *node, int idx);
+
 /** Returns the info string from a fenced code block.
  */
 CMARK_GFM_EXPORT const char *cmark_node_get_fence_info(cmark_node *node);
diff --git a/ext/commonmarker/cmark-gfm_version.h b/ext/commonmarker/cmark-gfm_version.h
index e2bbfbbb..19e67d81 100644
--- a/ext/commonmarker/cmark-gfm_version.h
+++ b/ext/commonmarker/cmark-gfm_version.h
@@ -1,7 +1,7 @@
 #ifndef CMARK_GFM_VERSION_H
 #define CMARK_GFM_VERSION_H
 
-#define CMARK_GFM_VERSION ((0 << 24) | (29 << 16) | (0 << 8) | 6)
-#define CMARK_GFM_VERSION_STRING "0.29.0.gfm.6"
+#define CMARK_GFM_VERSION ((0 << 24) | (29 << 16) | (0 << 8) | 11)
+#define CMARK_GFM_VERSION_STRING "0.29.0.gfm.11"
 
 #endif
diff --git a/ext/commonmarker/cmark-upstream b/ext/commonmarker/cmark-upstream
index 57d5e093..1e230827 160000
--- a/ext/commonmarker/cmark-upstream
+++ b/ext/commonmarker/cmark-upstream
@@ -1 +1 @@
-Subproject commit 57d5e093ef801f54bf4174c900f7a863599bb47d
+Subproject commit 1e230827a584ebc9938c3eadc5059c55ef3c9abf
diff --git a/ext/commonmarker/cmark.c b/ext/commonmarker/cmark.c
index b3fad4b0..68c40c47 100644
--- a/ext/commonmarker/cmark.c
+++ b/ext/commonmarker/cmark.c
@@ -10,9 +10,9 @@
 cmark_node_type CMARK_NODE_LAST_BLOCK = CMARK_NODE_FOOTNOTE_DEFINITION;
 cmark_node_type CMARK_NODE_LAST_INLINE = CMARK_NODE_FOOTNOTE_REFERENCE;
 
-int cmark_version() { return CMARK_GFM_VERSION; }
+int cmark_version(void) { return CMARK_GFM_VERSION; }
 
-const char *cmark_version_string() { return CMARK_GFM_VERSION_STRING; }
+const char *cmark_version_string(void) { return CMARK_GFM_VERSION_STRING; }
 
 static void *xcalloc(size_t nmem, size_t size) {
   void *ptr = calloc(nmem, size);
@@ -38,7 +38,7 @@ static void xfree(void *ptr) {
 
 cmark_mem CMARK_DEFAULT_MEM_ALLOCATOR = {xcalloc, xrealloc, xfree};
 
-cmark_mem *cmark_get_default_mem_allocator() {
+cmark_mem *cmark_get_default_mem_allocator(void) {
   return &CMARK_DEFAULT_MEM_ALLOCATOR;
 }
 
diff --git a/ext/commonmarker/commonmark.c b/ext/commonmarker/commonmark.c
index 2e071944..4815bfc3 100644
--- a/ext/commonmarker/commonmark.c
+++ b/ext/commonmarker/commonmark.c
@@ -153,23 +153,8 @@ static bool is_autolink(cmark_node *node) {
                   link_text->as.literal.len) == 0);
 }
 
-// if node is a block node, returns node.
-// otherwise returns first block-level node that is an ancestor of node.
-// if there is no block-level ancestor, returns NULL.
-static cmark_node *get_containing_block(cmark_node *node) {
-  while (node) {
-    if (CMARK_NODE_BLOCK_P(node)) {
-      return node;
-    } else {
-      node = node->parent;
-    }
-  }
-  return NULL;
-}
-
 static int S_render_node(cmark_renderer *renderer, cmark_node *node,
                          cmark_event_type ev_type, int options) {
-  cmark_node *tmp;
   int list_number;
   cmark_delim_type list_delim;
   int numticks;
@@ -189,14 +174,17 @@ static int S_render_node(cmark_renderer *renderer, cmark_node *node,
   // Don't adjust tight list status til we've started the list.
   // Otherwise we loose the blank line between a paragraph and
   // a following list.
-  if (!(node->type == CMARK_NODE_ITEM && node->prev == NULL && entering)) {
-    tmp = get_containing_block(node);
-    renderer->in_tight_list_item =
-        tmp && // tmp might be NULL if there is no containing block
-        ((tmp->type == CMARK_NODE_ITEM &&
-          cmark_node_get_list_tight(tmp->parent)) ||
-         (tmp && tmp->parent && tmp->parent->type == CMARK_NODE_ITEM &&
-          cmark_node_get_list_tight(tmp->parent->parent)));
+  if (entering) {
+    if (node->parent && node->parent->type == CMARK_NODE_ITEM) {
+      renderer->in_tight_list_item = node->parent->parent->as.list.tight;
+    }
+  } else {
+    if (node->type == CMARK_NODE_LIST) {
+      renderer->in_tight_list_item =
+        node->parent &&
+        node->parent->type == CMARK_NODE_ITEM &&
+        node->parent->parent->as.list.tight;
+    }
   }
 
   if (node->extension && node->extension->commonmark_render_func) {
@@ -234,13 +222,8 @@ static int S_render_node(cmark_renderer *renderer, cmark_node *node,
     if (cmark_node_get_list_type(node->parent) == CMARK_BULLET_LIST) {
       marker_width = 4;
     } else {
-      list_number = cmark_node_get_list_start(node->parent);
+      list_number = cmark_node_get_item_index(node);
       list_delim = cmark_node_get_list_delim(node->parent);
-      tmp = node;
-      while (tmp->prev) {
-        tmp = tmp->prev;
-        list_number += 1;
-      }
       // we ensure a width of at least 4 so
       // we get nice transition from single digits
       // to double
@@ -405,10 +388,12 @@ static int S_render_node(cmark_renderer *renderer, cmark_node *node,
     break;
 
   case CMARK_NODE_STRONG:
-    if (entering) {
-      LIT("**");
-    } else {
-      LIT("**");
+    if (node->parent == NULL || node->parent->type != CMARK_NODE_STRONG) {
+      if (entering) {
+        LIT("**");
+      } else {
+        LIT("**");
+      }
     }
     break;
 
diff --git a/ext/commonmarker/html.c b/ext/commonmarker/html.c
index 12d3c3e9..22513c93 100644
--- a/ext/commonmarker/html.c
+++ b/ext/commonmarker/html.c
@@ -63,10 +63,16 @@ static bool S_put_footnote_backref(cmark_html_renderer *renderer, cmark_strbuf *
   if (renderer->written_footnote_ix >= renderer->footnote_ix)
     return false;
   renderer->written_footnote_ix = renderer->footnote_ix;
+  char m[32];
+  snprintf(m, sizeof(m), "%d", renderer->written_footnote_ix);
 
   cmark_strbuf_puts(html, "<a href=\"#fnref-");
   houdini_escape_href(html, node->as.literal.data, node->as.literal.len);
-  cmark_strbuf_puts(html, "\" class=\"footnote-backref\" data-footnote-backref aria-label=\"Back to content\">↩</a>");
+  cmark_strbuf_puts(html, "\" class=\"footnote-backref\" data-footnote-backref data-footnote-backref-idx=\"");
+  cmark_strbuf_puts(html, m);
+  cmark_strbuf_puts(html, "\" aria-label=\"Back to reference ");
+  cmark_strbuf_puts(html, m);
+  cmark_strbuf_puts(html, "\">↩</a>");
 
   if (node->footnote.def_count > 1)
   {
@@ -78,7 +84,15 @@ static bool S_put_footnote_backref(cmark_html_renderer *renderer, cmark_strbuf *
       houdini_escape_href(html, node->as.literal.data, node->as.literal.len);
       cmark_strbuf_puts(html, "-");
       cmark_strbuf_puts(html, n);
-      cmark_strbuf_puts(html, "\" class=\"footnote-backref\" data-footnote-backref aria-label=\"Back to content\">↩<sup class=\"footnote-ref\">");
+      cmark_strbuf_puts(html, "\" class=\"footnote-backref\" data-footnote-backref data-footnote-backref-idx=\"");
+      cmark_strbuf_puts(html, m);
+      cmark_strbuf_puts(html, "-");
+      cmark_strbuf_puts(html, n);
+      cmark_strbuf_puts(html, "\" aria-label=\"Back to reference ");
+      cmark_strbuf_puts(html, m);
+      cmark_strbuf_puts(html, "-");
+      cmark_strbuf_puts(html, n);
+      cmark_strbuf_puts(html, "\">↩<sup class=\"footnote-ref\">");
       cmark_strbuf_puts(html, n);
       cmark_strbuf_puts(html, "</sup></a>");
     }
@@ -350,10 +364,12 @@ static int S_render_node(cmark_html_renderer *renderer, cmark_node *node,
     break;
 
   case CMARK_NODE_STRONG:
-    if (entering) {
-      cmark_strbuf_puts(html, "<strong>");
-    } else {
-      cmark_strbuf_puts(html, "</strong>");
+    if (node->parent == NULL || node->parent->type != CMARK_NODE_STRONG) {
+      if (entering) {
+        cmark_strbuf_puts(html, "<strong>");
+      } else {
+        cmark_strbuf_puts(html, "</strong>");
+      }
     }
     break;
 
diff --git a/ext/commonmarker/latex.c b/ext/commonmarker/latex.c
index 8be15b0d..1a6367a4 100644
--- a/ext/commonmarker/latex.c
+++ b/ext/commonmarker/latex.c
@@ -385,10 +385,12 @@ static int S_render_node(cmark_renderer *renderer, cmark_node *node,
     break;
 
   case CMARK_NODE_STRONG:
-    if (entering) {
-      LIT("\\textbf{");
-    } else {
-      LIT("}");
+    if (node->parent == NULL || node->parent->type != CMARK_NODE_STRONG) {
+      if (entering) {
+        LIT("\\textbf{");
+      } else {
+        LIT("}");
+      }
     }
     break;
 
diff --git a/ext/commonmarker/man.c b/ext/commonmarker/man.c
index 441a96e4..634fd9d0 100644
--- a/ext/commonmarker/man.c
+++ b/ext/commonmarker/man.c
@@ -74,7 +74,6 @@ static void S_outc(cmark_renderer *renderer, cmark_node *node,
 
 static int S_render_node(cmark_renderer *renderer, cmark_node *node,
                          cmark_event_type ev_type, int options) {
-  cmark_node *tmp;
   int list_number;
   bool entering = (ev_type == CMARK_EVENT_ENTER);
   bool allow_wrap = renderer->width > 0 && !(CMARK_OPT_NOBREAKS & options);
@@ -123,12 +122,7 @@ static int S_render_node(cmark_renderer *renderer, cmark_node *node,
       if (cmark_node_get_list_type(node->parent) == CMARK_BULLET_LIST) {
         LIT("\\[bu] 2");
       } else {
-        list_number = cmark_node_get_list_start(node->parent);
-        tmp = node;
-        while (tmp->prev) {
-          tmp = tmp->prev;
-          list_number += 1;
-        }
+        list_number = cmark_node_get_item_index(node);
         char list_number_s[LIST_NUMBER_SIZE];
         snprintf(list_number_s, LIST_NUMBER_SIZE, "\"%d.\" 4", list_number);
         LIT(list_number_s);
@@ -225,10 +219,12 @@ static int S_render_node(cmark_renderer *renderer, cmark_node *node,
     break;
 
   case CMARK_NODE_STRONG:
-    if (entering) {
-      LIT("\\f[B]");
-    } else {
-      LIT("\\f[]");
+    if (node->parent == NULL || node->parent->type != CMARK_NODE_STRONG) {
+      if (entering) {
+        LIT("\\f[B]");
+      } else {
+        LIT("\\f[]");
+      }
     }
     break;
 
diff --git a/ext/commonmarker/node.c b/ext/commonmarker/node.c
index 80c434e3..67f657d8 100644
--- a/ext/commonmarker/node.c
+++ b/ext/commonmarker/node.c
@@ -5,16 +5,22 @@
 #include "node.h"
 #include "syntax_extension.h"
 
+/**
+ * Expensive safety checks are off by default, but can be enabled
+ * by calling cmark_enable_safety_checks().
+ */
+static bool enable_safety_checks = false;
+
+void cmark_enable_safety_checks(bool enable) {
+  enable_safety_checks = enable;
+}
+
 static void S_node_unlink(cmark_node *node);
 
 #define NODE_MEM(node) cmark_node_mem(node)
 
-cmark_node__internal_flags CMARK_NODE__OPEN;
-cmark_node__internal_flags CMARK_NODE__LAST_LINE_BLANK;
-cmark_node__internal_flags CMARK_NODE__LAST_LINE_CHECKED;
-
-void cmark_register_node_flag(cmark_node__internal_flags *flags) {
-  static uint8_t shift = 0;
+void cmark_register_node_flag(cmark_node_internal_flags *flags) {
+  static cmark_node_internal_flags nextflag = CMARK_NODE__REGISTER_FIRST;
 
   // flags should be a pointer to a global variable and this function
   // should only be called once to initialize its value.
@@ -24,24 +30,16 @@ void cmark_register_node_flag(cmark_node__internal_flags *flags) {
   }
 
   // Check that we haven't run out of bits.
-  if (shift >= 8 * sizeof(cmark_node__internal_flags)) {
+  if (nextflag == 0) {
     fprintf(stderr, "too many flags in cmark_register_node_flag\n");
     abort();
   }
 
-  *flags = (cmark_node__internal_flags)1 << shift;
-  shift++;
+  *flags = nextflag;
+  nextflag <<= 1;
 }
 
-void cmark_init_standard_node_flags() {
-  static int initialized = 0;
-  if (!initialized) {
-    initialized = 1;
-    cmark_register_node_flag(&CMARK_NODE__OPEN);
-    cmark_register_node_flag(&CMARK_NODE__LAST_LINE_BLANK);
-    cmark_register_node_flag(&CMARK_NODE__LAST_LINE_CHECKED);
-  }
-}
+void cmark_init_standard_node_flags(void) {}
 
 bool cmark_node_can_contain_type(cmark_node *node, cmark_node_type child_type) {
   if (child_type == CMARK_NODE_DOCUMENT) {
@@ -82,8 +80,6 @@ bool cmark_node_can_contain_type(cmark_node *node, cmark_node_type child_type) {
 }
 
 static bool S_can_contain(cmark_node *node, cmark_node *child) {
-  cmark_node *cur;
-
   if (node == NULL || child == NULL) {
     return false;
   }
@@ -91,14 +87,16 @@ static bool S_can_contain(cmark_node *node, cmark_node *child) {
     return 0;
   }
 
-  // Verify that child is not an ancestor of node or equal to node.
-  cur = node;
-  do {
-    if (cur == child) {
-      return false;
-    }
-    cur = cur->parent;
-  } while (cur != NULL);
+  if (enable_safety_checks) {
+    // Verify that child is not an ancestor of node or equal to node.
+    cmark_node *cur = node;
+    do {
+      if (cur == child) {
+        return false;
+      }
+      cur = cur->parent;
+    } while (cur != NULL);
+  }
 
   return cmark_node_can_contain_type(node, (cmark_node_type) child->type);
 }
@@ -335,6 +333,14 @@ cmark_node *cmark_node_last_child(cmark_node *node) {
   }
 }
 
+cmark_node *cmark_node_parent_footnote_def(cmark_node *node) {
+  if (node == NULL) {
+    return NULL;
+  } else {
+    return node->parent_footnote_def;
+  }
+}
+
 void *cmark_node_get_user_data(cmark_node *node) {
   if (node == NULL) {
     return NULL;
@@ -558,6 +564,31 @@ int cmark_node_set_list_tight(cmark_node *node, int tight) {
   }
 }
 
+int cmark_node_get_item_index(cmark_node *node) {
+  if (node == NULL) {
+    return 0;
+  }
+
+  if (node->type == CMARK_NODE_ITEM) {
+    return node->as.list.start;
+  } else {
+    return 0;
+  }
+}
+
+int cmark_node_set_item_index(cmark_node *node, int idx) {
+  if (node == NULL || idx < 0) {
+    return 0;
+  }
+
+  if (node->type == CMARK_NODE_ITEM) {
+    node->as.list.start = idx;
+    return 1;
+  } else {
+    return 0;
+  }
+}
+
 const char *cmark_node_get_fence_info(cmark_node *node) {
   if (node == NULL) {
     return NULL;
diff --git a/ext/commonmarker/node.h b/ext/commonmarker/node.h
index 281258f7..38ac4a6f 100644
--- a/ext/commonmarker/node.h
+++ b/ext/commonmarker/node.h
@@ -48,7 +48,17 @@ typedef struct {
   cmark_chunk on_exit;
 } cmark_custom;
 
-typedef uint16_t cmark_node__internal_flags;
+enum cmark_node__internal_flags {
+  CMARK_NODE__OPEN = (1 << 0),
+  CMARK_NODE__LAST_LINE_BLANK = (1 << 1),
+  CMARK_NODE__LAST_LINE_CHECKED = (1 << 2),
+
+  // Extensions can register custom flags by calling `cmark_register_node_flag`.
+  // This is the starting value for the custom flags.
+  CMARK_NODE__REGISTER_FIRST = (1 << 3),
+};
+
+typedef uint16_t cmark_node_internal_flags;
 
 struct cmark_node {
   cmark_strbuf content;
@@ -68,10 +78,18 @@ struct cmark_node {
   int end_column;
   int internal_offset;
   uint16_t type;
-  cmark_node__internal_flags flags;
+  cmark_node_internal_flags flags;
 
   cmark_syntax_extension *extension;
 
+  /**
+   * Used during cmark_render() to cache the most recent non-NULL
+   * extension, if you go up the parent chain like this:
+   *
+   * node->parent->...parent->extension
+   */
+  cmark_syntax_extension *ancestor_extension;
+
   union {
     int ref_ix;
     int def_count;
@@ -98,22 +116,18 @@ struct cmark_node {
  * which will store the flag value.
  */
 CMARK_GFM_EXPORT
-void cmark_register_node_flag(cmark_node__internal_flags *flags);
+void cmark_register_node_flag(cmark_node_internal_flags *flags);
 
 /**
- * Standard node flags. (Initialized using `cmark_init_standard_node_flags`.)
- */
-extern cmark_node__internal_flags CMARK_NODE__OPEN;
-extern cmark_node__internal_flags CMARK_NODE__LAST_LINE_BLANK;
-extern cmark_node__internal_flags CMARK_NODE__LAST_LINE_CHECKED;
-
-/**
- * Uses `cmark_register_node_flag` to initialize the standard node flags.
- * This function should be called at program startup time. Calling it
- * multiple times has no additional effect.
+ * DEPRECATED.
+ *
+ * This function was added in cmark-gfm version 0.29.0.gfm.7, and was
+ * required to be called at program start time, which caused
+ * backwards-compatibility issues in applications that use cmark-gfm as a
+ * library. It is now a no-op.
  */
 CMARK_GFM_EXPORT
-void cmark_init_standard_node_flags();
+void cmark_init_standard_node_flags(void);
 
 static CMARK_INLINE cmark_mem *cmark_node_mem(cmark_node *node) {
   return node->content.mem;
@@ -138,6 +152,13 @@ static CMARK_INLINE bool CMARK_NODE_INLINE_P(cmark_node *node) {
 
 CMARK_GFM_EXPORT bool cmark_node_can_contain_type(cmark_node *node, cmark_node_type child_type);
 
+/**
+ * Enable (or disable) extra safety checks. These extra checks cause
+ * extra performance overhead (in some cases quadratic), so they are only
+ * intended to be used during testing.
+ */
+CMARK_GFM_EXPORT void cmark_enable_safety_checks(bool enable);
+
 #ifdef __cplusplus
 }
 #endif
diff --git a/ext/commonmarker/plaintext.c b/ext/commonmarker/plaintext.c
index b25e4a39..0c7d257b 100644
--- a/ext/commonmarker/plaintext.c
+++ b/ext/commonmarker/plaintext.c
@@ -16,23 +16,8 @@ static CMARK_INLINE void outc(cmark_renderer *renderer, cmark_node *node,
   cmark_render_code_point(renderer, c);
 }
 
-// if node is a block node, returns node.
-// otherwise returns first block-level node that is an ancestor of node.
-// if there is no block-level ancestor, returns NULL.
-static cmark_node *get_containing_block(cmark_node *node) {
-  while (node) {
-    if (CMARK_NODE_BLOCK_P(node)) {
-      return node;
-    } else {
-      node = node->parent;
-    }
-  }
-  return NULL;
-}
-
 static int S_render_node(cmark_renderer *renderer, cmark_node *node,
                          cmark_event_type ev_type, int options) {
-  cmark_node *tmp;
   int list_number;
   cmark_delim_type list_delim;
   int i;
@@ -46,14 +31,17 @@ static int S_render_node(cmark_renderer *renderer, cmark_node *node,
   // Don't adjust tight list status til we've started the list.
   // Otherwise we loose the blank line between a paragraph and
   // a following list.
-  if (!(node->type == CMARK_NODE_ITEM && node->prev == NULL && entering)) {
-    tmp = get_containing_block(node);
-    renderer->in_tight_list_item =
-        tmp && // tmp might be NULL if there is no containing block
-        ((tmp->type == CMARK_NODE_ITEM &&
-          cmark_node_get_list_tight(tmp->parent)) ||
-         (tmp && tmp->parent && tmp->parent->type == CMARK_NODE_ITEM &&
-          cmark_node_get_list_tight(tmp->parent->parent)));
+  if (entering) {
+    if (node->parent && node->parent->type == CMARK_NODE_ITEM) {
+      renderer->in_tight_list_item = node->parent->parent->as.list.tight;
+    }
+  } else {
+    if (node->type == CMARK_NODE_LIST) {
+      renderer->in_tight_list_item =
+        node->parent &&
+        node->parent->type == CMARK_NODE_ITEM &&
+        node->parent->parent->as.list.tight;
+    }
   }
 
   if (node->extension && node->extension->plaintext_render_func) {
@@ -79,13 +67,8 @@ static int S_render_node(cmark_renderer *renderer, cmark_node *node,
     if (cmark_node_get_list_type(node->parent) == CMARK_BULLET_LIST) {
       marker_width = 4;
     } else {
-      list_number = cmark_node_get_list_start(node->parent);
+      list_number = cmark_node_get_item_index(node);
       list_delim = cmark_node_get_list_delim(node->parent);
-      tmp = node;
-      while (tmp->prev) {
-        tmp = tmp->prev;
-        list_number += 1;
-      }
       // we ensure a width of at least 4 so
       // we get nice transition from single digits
       // to double
diff --git a/ext/commonmarker/render.c b/ext/commonmarker/render.c
index 02e9e838..1a0d2ae8 100644
--- a/ext/commonmarker/render.c
+++ b/ext/commonmarker/render.c
@@ -31,13 +31,7 @@ static void S_out(cmark_renderer *renderer, cmark_node *node,
   cmark_chunk remainder = cmark_chunk_literal("");
   int k = renderer->buffer->size - 1;
 
-  cmark_syntax_extension *ext = NULL;
-  cmark_node *n = node;
-  while (n && !ext) {
-    ext = n->extension;
-    if (!ext)
-      n = n->parent;
-  }
+  cmark_syntax_extension *ext = node->ancestor_extension;
   if (ext && !ext->commonmark_escape_func)
     ext = NULL;
 
@@ -182,6 +176,20 @@ char *cmark_render(cmark_mem *mem, cmark_node *root, int options, int width,
 
   while ((ev_type = cmark_iter_next(iter)) != CMARK_EVENT_DONE) {
     cur = cmark_iter_get_node(iter);
+    if (cur->extension) {
+      cur->ancestor_extension = cur->extension;
+    } else if (cur->parent) {
+      cur->ancestor_extension = cur->parent->ancestor_extension;
+    }
+    if (cur->type == CMARK_NODE_ITEM) {
+      // Calculate the list item's index, for the benefit of output formats
+      // like commonmark and plaintext.
+      if (cur->prev) {
+        cmark_node_set_item_index(cur, 1 + cmark_node_get_item_index(cur->prev));
+      } else {
+        cmark_node_set_item_index(cur, cmark_node_get_list_start(cur->parent));
+      }
+    }
     if (!render_node(&renderer, cur, ev_type, options)) {
       // a false value causes us to skip processing
       // the node's contents.  this is used for
diff --git a/ext/commonmarker/table.c b/ext/commonmarker/table.c
index 7f281322..e53ea315 100644
--- a/ext/commonmarker/table.c
+++ b/ext/commonmarker/table.c
@@ -12,7 +12,7 @@
 #include "cmark-gfm-core-extensions.h"
 
 // Custom node flag, initialized in `create_table_extension`.
-static cmark_node__internal_flags CMARK_NODE__TABLE_VISITED;
+static cmark_node_internal_flags CMARK_NODE__TABLE_VISITED;
 
 cmark_node_type CMARK_NODE_TABLE, CMARK_NODE_TABLE_ROW,
     CMARK_NODE_TABLE_CELL;
diff --git a/ext/commonmarker/xml.c b/ext/commonmarker/xml.c
index 2975bf96..5753e5ab 100644
--- a/ext/commonmarker/xml.c
+++ b/ext/commonmarker/xml.c
@@ -11,6 +11,7 @@
 #include "syntax_extension.h"
 
 #define BUFFER_SIZE 100
+#define MAX_INDENT 40
 
 // Functions to convert cmark_nodes to XML strings.
 
@@ -26,7 +27,7 @@ struct render_state {
 
 static CMARK_INLINE void indent(struct render_state *state) {
   int i;
-  for (i = 0; i < state->indent; i++) {
+  for (i = 0; i < state->indent && i < MAX_INDENT; i++) {
     cmark_strbuf_putc(state->xml, ' ');
   }
 }
diff --git a/lib/commonmarker/renderer/html_renderer.rb b/lib/commonmarker/renderer/html_renderer.rb
index df10042d..2d8375ab 100644
--- a/lib/commonmarker/renderer/html_renderer.rb
+++ b/lib/commonmarker/renderer/html_renderer.rb
@@ -129,8 +129,12 @@ def emph(_)
       out("<em>", :children, "</em>")
     end
 
-    def strong(_)
-      out("<strong>", :children, "</strong>")
+    def strong(node)
+      if node.parent&.type == :strong
+        out(:children)
+      else
+        out("<strong>", :children, "</strong>")
+      end
     end
 
     def link(node)
diff --git a/lib/commonmarker/version.rb b/lib/commonmarker/version.rb
index 7d03a7ea..77032fd8 100644
--- a/lib/commonmarker/version.rb
+++ b/lib/commonmarker/version.rb
@@ -1,5 +1,5 @@
 # frozen_string_literal: true
 
 module CommonMarker
-  VERSION = "0.23.7"
+  VERSION = "0.23.9"
 end
diff --git a/test/test_footnotes.rb b/test/test_footnotes.rb
index 7cdfd93a..0e00a913 100644
--- a/test/test_footnotes.rb
+++ b/test/test_footnotes.rb
@@ -13,7 +13,7 @@ def test_to_html
       <section class="footnotes" data-footnotes>
       <ol>
       <li id="fn-hi">
-      <p>Hey! <a href="#fnref-hi" class="footnote-backref" data-footnote-backref aria-label="Back to content">↩</a></p>
+      <p>Hey! <a href="#fnref-hi" class="footnote-backref" data-footnote-backref data-footnote-backref-idx="1" aria-label="Back to reference 1">↩</a></p>
       </li>
       </ol>
       </section>
@@ -50,7 +50,7 @@ def test_render_html
       <section class="footnotes" data-footnotes>
       <ol>
       <li id="fn-1">
-      <p>This is a footnote <a href="#fnref-1" class="footnote-backref" data-footnote-backref aria-label="Back to content">↩</a></p>
+      <p>This is a footnote <a href="#fnref-1" class="footnote-backref" data-footnote-backref data-footnote-backref-idx="1" aria-label="Back to reference 1">↩</a></p>
       </li>
       </ol>
       </section>