fix: update link reference

Author: lepture

src/mistune/helpers.py

@@ -19,8 +19,8 @@
 
 LINK_TITLE_RE = re.compile(
     r"[ \t\n]+("
-    r'"(?:\\' + PUNCTUATION + r'|[^"\x00])*"|'  # "title"
-    r"'(?:\\" + PUNCTUATION + r"|[^'\x00])*'"  # 'title'
+    r'"(?:\\' + PUNCTUATION + r'|[^"\\\x00])*"|'
+    r"'(?:\\" + PUNCTUATION + r"|[^'\\\x00])*'"
     r")"
 )
 PAREN_END_RE = re.compile(r"\s*\)")

tests/test_commonmark.py

@@ -18,6 +18,7 @@
     # we don't support link title in (title)
     "links_496",
     "links_504",
+    "link_reference_definitions_202",
     # we don't support flanking delimiter run
     "emphasis_and_strong_emphasis_352",
     "emphasis_and_strong_emphasis_367",