document TokenError and unclosed expression behavior (closes #12063)

Patch by Amandine Lee.
diff --git a/Doc/library/tokenize.rst b/Doc/library/tokenize.rst
index 37d9f41..bd6b121 100644
--- a/Doc/library/tokenize.rst
+++ b/Doc/library/tokenize.rst
@@ -131,6 +131,24 @@
 
    .. versionadded:: 3.2
 
+.. exception:: TokenError
+
+   Raised when either a docstring or expression that may be split over several
+   lines is not completed anywhere in the file, for example::
+
+      """Beginning of
+      docstring
+
+   or::
+
+      [1,
+       2,
+       3
+
+Note that unclosed single-quoted strings do not cause an error to be
+raised. They are tokenized as ``ERRORTOKEN``, followed by the tokenization of
+their contents.
+
 
 .. _tokenize-cli:
 
diff --git a/Misc/ACKS b/Misc/ACKS
index 344a29b..5f1a1dd 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -749,6 +749,7 @@
 Chris Lawrence
 Brian Leair
 Mathieu Leduc-Hamel
+Amandine Lee
 Antony Lee
 Christopher Lee
 Inyeol Lee