Revert the fix for #1548891, it broke backwards compatibility with arbitrary read buffers.
Fixes #1730114.
(backport from rev. 56830)
diff --git a/Doc/lib/libstringio.tex b/Doc/lib/libstringio.tex
index 2431251..73ff0e4 100644
--- a/Doc/lib/libstringio.tex
+++ b/Doc/lib/libstringio.tex
@@ -78,6 +78,10 @@
module, those provided by this module are not able to accept Unicode
strings that cannot be encoded as plain \ASCII{} strings.
+Calling \function{StringIO()} with a Unicode string parameter populates
+the object with the buffer representation of the Unicode string, instead of
+encoding the string.
+
Another difference from the \refmodule{StringIO} module is that calling
\function{StringIO()} with a string parameter creates a read-only object.
Unlike an object created without a string parameter, it does not have