diff --git a/CppCoreGuidelines.md b/CppCoreGuidelines.md
index 0b884cc..a252c95 100644
--- a/CppCoreGuidelines.md
+++ b/CppCoreGuidelines.md
@@ -20308,6 +20308,14 @@ For writing to a file, there is rarely a need to `flush`.
 
 ##### Note
 
+For string streams (specifically `ostringstream`), the insertion of an `endl` is entirely equivalent
+to the insertion of a `'\n'` character, but also in this case, `endl` might be significantly slower.
+
+`endl` does *not* take care of producing a platform specific end-of-line sequence (like "\r\n" on
+Windows). So for a string stream, `s << endl` just inserts a *single* character, `'\n'`.
+
+##### Note
+
 Apart from the (occasionally important) issue of performance,
 the choice between `'\n'` and `endl` is almost completely aesthetic.
 
diff --git a/scripts/hunspell/isocpp.dic b/scripts/hunspell/isocpp.dic
index ef45e4e..e9d90e5 100644
--- a/scripts/hunspell/isocpp.dic
+++ b/scripts/hunspell/isocpp.dic
@@ -389,6 +389,7 @@ optimizable
 O'Reilly
 org
 ostream
+ostringstream
 overabstract
 overconstrain
 overconstrained