Note that backslash escaping has changed in some places

CHANGELOG.md

@@ -25,6 +25,19 @@ Major Changes:
    They will retain the value of `None`.  To go back to the old behaviour, you can override
    the `null_representation` setting to an empty string in your config file or by setting the
    `ANSIBLE_NULL_REPRESENTATION` environment variable.
+ * backslashes used when specifying parameters in jinja2 expressions in YAML
+   dicts sometimes needed to be escaped twice.  This has been fixed so that
+   escaping once works.  Here's an example of how playbooks need to be modified::
+
+     # Syntax in 1.9.x
+     - debug:
+         msg: "{{ 'test1_junk 1\\\\3' | regex_replace('(.*)_junk (.*)', '\\\\1 \\\\2') }}"
+     # Syntax in 2.0.x
+     - debug:
+         msg: "{{ 'test1_junk 1\\3' | regex_replace('(.*)_junk (.*)', '\\1 \\2') }}"
+
+     # Output:
+     "msg": "test1 1\\3"
 
 Deprecated Modules (new ones in parens):
   * ec2_ami_search (ec2_ami_find)

docsite/rst/playbooks_filters.rst

@@ -448,13 +448,13 @@ To match strings against a regex, use the "match" or "search" filter::
 To replace text in a string with regex, use the "regex_replace" filter::
 
     # convert "ansible" to "able"    
-    {{ 'ansible' | regex_replace('^a.*i(.*)$', 'a\\1') }}         
+    {{ 'ansible' | regex_replace('^a.*i(.*)$', 'a\\1') }}
 
     # convert "foobar" to "bar"
     {{ 'foobar' | regex_replace('^f.*o(.*)$', '\\1') }}
 
-.. note:: If "regex_replace" filter is used with variables inside YAML arguments (as opposed to simpler 'key=value' arguments),
-   then you need to escape backreferences (e.g. ``\\1``) with 4 backslashes (``\\\\``) instead of 2 (``\\``).
+.. note:: Prior to ansible 2.0, if "regex_replace" filter was used with variables inside YAML arguments (as opposed to simpler 'key=value' arguments),
+   then you needed to escape backreferences (e.g. ``\\1``) with 4 backslashes (``\\\\``) instead of 2 (``\\``).
 
 To escape special characters within a regex, use the "regex_escape" filter::