Ticket #21316: mark_safe_21316.txt

diff --git a/docs/ref/utils.txt b/docs/ref/utils.txt
index e03a775..311871e 100644
--- a/docs/ref/utils.txt
+++ b/docs/ref/utils.txt
@@ -557,16 +557,16 @@ escaping HTML.
     So, instead of writing:
 
     .. code-block:: python
-
+       
         mark_safe(u"%s <b>%s</b> %s" % (some_html,
                                         escape(some_text),
                                         escape(some_other_text),
                                         ))
 
     you should instead use:
-
+       
     .. code-block:: python
-
+               
         format_html(u"{0} <b>{1}</b> {2}",
                     mark_safe(some_html), some_text, some_other_text)
 
@@ -722,7 +722,7 @@ Functions for working with Python modules.
         ImproperlyConfigured = import_by_path('django.core.exceptions.ImproperlyConfigured')
 
     is equivalent to::
-
+               
         from django.core.exceptions import ImproperlyConfigured
 
 ``django.utils.safestring``
@@ -763,7 +763,19 @@ appropriate entities.
     object can be used everywhere a string or unicode object is appropriate.
 
     Can be called multiple times on a single string.
-
+    String marked safe will become unsafe again if modified.
+       
+    For example::
+    
+               mystr = '<b>Hello World</b>   '
+               mystr = mark_safe(mystr)
+               type(mystr)
+               <class 'django.utils.safestring.SafeBytes'>
+               
+               mystr = mystr.strip() #removing white-spaces
+               type(mystr)
+               <type 'str'>
+       
 .. function:: mark_for_escaping(s)
 
     Explicitly mark a string as requiring HTML escaping upon output. Has no