diff --git a/Doc/lib/libstdtypes.tex b/Doc/lib/libstdtypes.tex
index b638fa3..3e9cc53 100644
--- a/Doc/lib/libstdtypes.tex
+++ b/Doc/lib/libstdtypes.tex
@@ -586,6 +586,11 @@
 
 \subsubsection{String Formatting Operations \label{typesseq-strings}}
 
+\index{formatting, string}
+\index{string!formatting}
+\index{printf-style formatting}
+\index{sprintf-style formatting}
+
 String objects have one unique built-in operation: the \code{\%}
 operator (modulo) with a string left argument interprets this string
 as a C \cfunction{sprintf()} format string to be applied to the