Move UserString to collections.
Removed decode() method.  Added isidentifier() and format() methods.
Drop MutableUserString class.
diff --git a/Lib/collections.py b/Lib/collections.py
index 93194e0..dafc5e5 100644
--- a/Lib/collections.py
+++ b/Lib/collections.py
@@ -237,6 +237,150 @@
 
 
 ################################################################################
+### UserString
+################################################################################
+
+class UserString(Sequence):
+    def __init__(self, seq):
+        if isinstance(seq, str):
+            self.data = seq
+        elif isinstance(seq, UserString):
+            self.data = seq.data[:]
+        else:
+            self.data = str(seq)
+    def __str__(self): return str(self.data)
+    def __repr__(self): return repr(self.data)
+    def __int__(self): return int(self.data)
+    def __long__(self): return int(self.data)
+    def __float__(self): return float(self.data)
+    def __complex__(self): return complex(self.data)
+    def __hash__(self): return hash(self.data)
+
+    def __eq__(self, string):
+        if isinstance(string, UserString):
+            return self.data == string.data
+        return self.data == string
+    def __ne__(self, string):
+        if isinstance(string, UserString):
+            return self.data != string.data
+        return self.data != string
+    def __lt__(self, string):
+        if isinstance(string, UserString):
+            return self.data < string.data
+        return self.data < string
+    def __le__(self, string):
+        if isinstance(string, UserString):
+            return self.data <= string.data
+        return self.data <= string
+    def __gt__(self, string):
+        if isinstance(string, UserString):
+            return self.data > string.data
+        return self.data > string
+    def __ge__(self, string):
+        if isinstance(string, UserString):
+            return self.data >= string.data
+        return self.data >= string
+
+    def __contains__(self, char):
+        if isinstance(char, UserString):
+            char = char.data
+        return char in self.data
+
+    def __len__(self): return len(self.data)
+    def __getitem__(self, index): return self.__class__(self.data[index])
+    def __add__(self, other):
+        if isinstance(other, UserString):
+            return self.__class__(self.data + other.data)
+        elif isinstance(other, str):
+            return self.__class__(self.data + other)
+        return self.__class__(self.data + str(other))
+    def __radd__(self, other):
+        if isinstance(other, str):
+            return self.__class__(other + self.data)
+        return self.__class__(str(other) + self.data)
+    def __mul__(self, n):
+        return self.__class__(self.data*n)
+    __rmul__ = __mul__
+    def __mod__(self, args):
+        return self.__class__(self.data % args)
+
+    # the following methods are defined in alphabetical order:
+    def capitalize(self): return self.__class__(self.data.capitalize())
+    def center(self, width, *args):
+        return self.__class__(self.data.center(width, *args))
+    def count(self, sub, start=0, end=_sys.maxsize):
+        if isinstance(sub, UserString):
+            sub = sub.data
+        return self.data.count(sub, start, end)
+    def encode(self, encoding=None, errors=None): # XXX improve this?
+        if encoding:
+            if errors:
+                return self.__class__(self.data.encode(encoding, errors))
+            return self.__class__(self.data.encode(encoding))
+        return self.__class__(self.data.encode())
+    def endswith(self, suffix, start=0, end=_sys.maxsize):
+        return self.data.endswith(suffix, start, end)
+    def expandtabs(self, tabsize=8):
+        return self.__class__(self.data.expandtabs(tabsize))
+    def find(self, sub, start=0, end=_sys.maxsize):
+        if isinstance(sub, UserString):
+            sub = sub.data
+        return self.data.find(sub, start, end)
+    def format(self, *args, **kwds):
+        return self.data.format(*args, **kwds)
+    def index(self, sub, start=0, end=_sys.maxsize):
+        return self.data.index(sub, start, end)
+    def isalpha(self): return self.data.isalpha()
+    def isalnum(self): return self.data.isalnum()
+    def isdecimal(self): return self.data.isdecimal()
+    def isdigit(self): return self.data.isdigit()
+    def isidentifier(self): return self.data.isidentifier()
+    def islower(self): return self.data.islower()
+    def isnumeric(self): return self.data.isnumeric()
+    def isspace(self): return self.data.isspace()
+    def istitle(self): return self.data.istitle()
+    def isupper(self): return self.data.isupper()
+    def join(self, seq): return self.data.join(seq)
+    def ljust(self, width, *args):
+        return self.__class__(self.data.ljust(width, *args))
+    def lower(self): return self.__class__(self.data.lower())
+    def lstrip(self, chars=None): return self.__class__(self.data.lstrip(chars))
+    def partition(self, sep):
+        return self.data.partition(sep)
+    def replace(self, old, new, maxsplit=-1):
+        if isinstance(old, UserString):
+            old = old.data
+        if isinstance(new, UserString):
+            new = new.data
+        return self.__class__(self.data.replace(old, new, maxsplit))
+    def rfind(self, sub, start=0, end=_sys.maxsize):
+        return self.data.rfind(sub, start, end)
+    def rindex(self, sub, start=0, end=_sys.maxsize):
+        return self.data.rindex(sub, start, end)
+    def rjust(self, width, *args):
+        return self.__class__(self.data.rjust(width, *args))
+    def rpartition(self, sep):
+        return self.data.rpartition(sep)
+    def rstrip(self, chars=None):
+        return self.__class__(self.data.rstrip(chars))
+    def split(self, sep=None, maxsplit=-1):
+        return self.data.split(sep, maxsplit)
+    def rsplit(self, sep=None, maxsplit=-1):
+        return self.data.rsplit(sep, maxsplit)
+    def splitlines(self, keepends=0): return self.data.splitlines(keepends)
+    def startswith(self, prefix, start=0, end=_sys.maxsize):
+        return self.data.startswith(prefix, start, end)
+    def strip(self, chars=None): return self.__class__(self.data.strip(chars))
+    def swapcase(self): return self.__class__(self.data.swapcase())
+    def title(self): return self.__class__(self.data.title())
+    def translate(self, *args):
+        return self.__class__(self.data.translate(*args))
+    def upper(self): return self.__class__(self.data.upper())
+    def zfill(self, width): return self.__class__(self.data.zfill(width))
+
+
+
+################################################################################
 ### Simple tests
 ################################################################################