Index: forms/formsets.py
===================================================================
--- forms/formsets.py	(revision 8445)
+++ forms/formsets.py	(working copy)
@@ -28,7 +28,7 @@
     """
     A collection of instances of the same Form class.
     """
-    def __init__(self, data=None, files=None, auto_id='id_%s', prefix=None,
+    def __init__(self, data=None, files=None, auto_id='id-%s', prefix=None,
                  initial=None, error_class=ErrorList):
         self.is_bound = data is not None or files is not None
         self.prefix = prefix or 'form'
Index: forms/models.py
===================================================================
--- forms/models.py	(revision 8445)
+++ forms/models.py	(working copy)
@@ -184,7 +184,7 @@
         return new_class
 
 class BaseModelForm(BaseForm):
-    def __init__(self, data=None, files=None, auto_id='id_%s', prefix=None,
+    def __init__(self, data=None, files=None, auto_id='id-%s', prefix=None,
                  initial=None, error_class=ErrorList, label_suffix=':',
                  empty_permitted=False, instance=None):
         opts = self._meta
@@ -240,7 +240,7 @@
     """
     model = None
 
-    def __init__(self, data=None, files=None, auto_id='id_%s', prefix=None,
+    def __init__(self, data=None, files=None, auto_id='id-%s', prefix=None,
                  queryset=None, **kwargs):
         self.queryset = queryset
         defaults = {'data': data, 'files': files, 'auto_id': auto_id, 'prefix': prefix}
Index: forms/forms.py
===================================================================
--- forms/forms.py	(revision 8445)
+++ forms/forms.py	(working copy)
@@ -68,7 +68,7 @@
     # class is different than Form. See the comments by the Form class for more
     # information. Any improvements to the form API should be made to *this*
     # class, not to the Form class.
-    def __init__(self, data=None, files=None, auto_id='id_%s', prefix=None,
+    def __init__(self, data=None, files=None, auto_id='id-%s', prefix=None,
                  initial=None, error_class=ErrorList, label_suffix=':',
                  empty_permitted=False):
         self.is_bound = data is not None or files is not None