add missing definitin of longstringitem
diff --git a/Doc/ref/ref2.tex b/Doc/ref/ref2.tex
index 2757ab1..9ccfee6 100644
--- a/Doc/ref/ref2.tex
+++ b/Doc/ref/ref2.tex
@@ -207,6 +207,7 @@
shortstring: "'" shortstringitem* "'" | '"' shortstringitem* '"'
longstring: "'''" longstringitem* "'''" | '"""' longstringitem* '"""'
shortstringitem: shortstringchar | escapeseq
+longstringitem: longstringchar | escapeseq
shortstringchar: <any ASCII character except "\" or newline or the quote>
longstringchar: <any ASCII character except "\">
escapeseq: "\" <any ASCII character>