A few additional unit tests based on the CommonMark spec.

src/comment.rs

@@ -2088,6 +2088,10 @@ fn main() {
         run_test("12) foo", "foo", 4, "12) ", "    ");
 
         run_test("    - foo", "foo", 6, "    - ", "      ");
+
+        // https://spec.commonmark.org/0.30 says: "A start number may begin with 0s":
+        run_test("0. foo", "foo", 3, "0. ", "   ");
+        run_test("01. foo", "foo", 4, "01. ", "    ");
     }
 
     #[test]
@@ -2108,9 +2112,20 @@ fn main() {
             // 1868. He was buried in...
             // ```
             "123.  only 2-digit numbers are recognized as item markers.",
-            // Parens.
+            // Parens:
             "123)  giving some coverage to parens as well.",
             "a)  giving some coverage to parens as well.",
+            // https://spec.commonmark.org/0.30 says that "at least one space or tab is needed
+            // between the list marker and any following content":
+            "1.Not a list item.",
+            "1.2.3. Not a list item.",
+            "1)Not a list item.",
+            "-Not a list item.",
+            "+Not a list item.",
+            "+1 not a list item.",
+            // https://spec.commonmark.org/0.30 says: "A start number may not be negative":
+            "-1. Not a list item.",
+            "-1 Not a list item.",
         ];
         for line in test_inputs.iter() {
             let maybe_block = ItemizedBlock::new(line);