diff --git a/lib/pure/collections/lists.nim b/lib/pure/collections/lists.nim
index 2770a3950f..095775cbbb 100644
--- a/lib/pure/collections/lists.nim
+++ b/lib/pure/collections/lists.nim
@@ -122,6 +122,22 @@ iterator items*[T](L: DoublyLinkedRing[T]): T =
   ## yields every value of `L`.
   itemsRingImpl()
 
+iterator mitems*[T](L: var DoublyLinkedList[T]): var T =
+  ## yields every value of `L` so that you can modify it.
+  itemsListImpl()
+
+iterator mitems*[T](L: var SinglyLinkedList[T]): var T =
+  ## yields every value of `L` so that you can modify it.
+  itemsListImpl()
+
+iterator mitems*[T](L: var SinglyLinkedRing[T]): var T =
+  ## yields every value of `L` so that you can modify it.
+  itemsRingImpl()
+
+iterator mitems*[T](L: var DoublyLinkedRing[T]): var T =
+  ## yields every value of `L` so that you can modify it.
+  itemsRingImpl()
+
 iterator nodes*[T](L: SinglyLinkedList[T]): SinglyLinkedNode[T] = 
   ## iterates over every node of `x`. Removing the current node from the
   ## list during traversal is supported.
diff --git a/lib/pure/collections/queues.nim b/lib/pure/collections/queues.nim
index fb4d35310a..af5e7b6cd7 100644
--- a/lib/pure/collections/queues.nim
+++ b/lib/pure/collections/queues.nim
@@ -39,6 +39,15 @@ iterator items*[T](q: Queue[T]): T =
     yield q.data[i]
     i = (i + 1) and q.mask
 
+iterator mitems*[T](q: var Queue[T]): var T =
+  ## yields every element of `q`.
+  var i = q.rd
+  var c = q.count
+  while c > 0:
+    dec c
+    yield q.data[i]
+    i = (i + 1) and q.mask
+
 proc add*[T](q: var Queue[T], item: T) =
   ## adds an `item` to the end of the queue `q`.
   var cap = q.mask+1
diff --git a/lib/pure/json.nim b/lib/pure/json.nim
index 733516bea2..873e4b78ee 100644
--- a/lib/pure/json.nim
+++ b/lib/pure/json.nim
@@ -872,12 +872,26 @@ iterator items*(node: JsonNode): JsonNode =
   for i in items(node.elems):
     yield i
 
+iterator mitems*(node: var JsonNode): var JsonNode =
+  ## Iterator for the items of `node`. `node` has to be a JArray. Items can be
+  ## modified.
+  assert node.kind == JArray
+  for i in mitems(node.elems):
+    yield i
+
 iterator pairs*(node: JsonNode): tuple[key: string, val: JsonNode] =
   ## Iterator for the child elements of `node`. `node` has to be a JObject.
   assert node.kind == JObject
   for key, val in items(node.fields):
     yield (key, val)
 
+iterator mpairs*(node: var JsonNode): var tuple[key: string, val: JsonNode] =
+  ## Iterator for the child elements of `node`. `node` has to be a JObject.
+  ## Items can be modified
+  assert node.kind == JObject
+  for keyVal in mitems(node.fields):
+    yield keyVal
+
 proc eat(p: var JsonParser, tok: TTokKind) = 
   if p.tok == tok: discard getTok(p)
   else: raiseParseErr(p, tokToStr[tok])
diff --git a/lib/pure/poly.nim b/lib/pure/poly.nim
index 286e5a8fda..58dcdc1ad7 100644
--- a/lib/pure/poly.nim
+++ b/lib/pure/poly.nim
@@ -58,7 +58,7 @@ proc `[]=` *(p:var Poly;idx:int,v:float)=
     
       
 iterator items*(p:Poly):float=
-  ## Iterates through the corfficients of the polynomial.
+  ## Iterates through the coefficients of the polynomial.
   var i=p.degree
   while i>=0:
     yield p[i]
diff --git a/lib/pure/xmltree.nim b/lib/pure/xmltree.nim
index 3c789d841c..c783158ea5 100644
--- a/lib/pure/xmltree.nim
+++ b/lib/pure/xmltree.nim
@@ -115,11 +115,21 @@ proc `[]`* (n: XmlNode, i: int): XmlNode {.inline.} =
   assert n.k == xnElement
   result = n.s[i]
 
+proc mget* (n: var XmlNode, i: int): var XmlNode {.inline.} = 
+  ## returns the `i`'th child of `n` so that it can be modified
+  assert n.k == xnElement
+  result = n.s[i]
+
 iterator items*(n: XmlNode): XmlNode {.inline.} = 
   ## iterates over any child of `n`.
   assert n.k == xnElement
   for i in 0 .. n.len-1: yield n[i]
 
+iterator mitems*(n: var XmlNode): var XmlNode {.inline.} = 
+  ## iterates over any child of `n`.
+  assert n.k == xnElement
+  for i in 0 .. n.len-1: yield mget(n, i)
+
 proc attrs*(n: XmlNode): XmlAttributes {.inline.} = 
   ## gets the attributes belonging to `n`.
   ## Returns `nil` if attributes have not been initialised for this node.
diff --git a/lib/system.nim b/lib/system.nim
index 69a77b89b6..12c5c63036 100644
--- a/lib/system.nim
+++ b/lib/system.nim
@@ -1653,6 +1653,13 @@ iterator items*[T](a: openArray[T]): T {.inline.} =
     yield a[i]
     inc(i)
 
+iterator mitems*[T](a: var openArray[T]): var T {.inline.} =
+  ## iterates over each item of `a` so that you can modify the yielded value.
+  var i = 0
+  while i < len(a):
+    yield a[i]
+    inc(i)
+
 iterator items*[IX, T](a: array[IX, T]): T {.inline.} =
   ## iterates over each item of `a`.
   var i = low(IX)
@@ -1662,6 +1669,15 @@ iterator items*[IX, T](a: array[IX, T]): T {.inline.} =
       if i >= high(IX): break
       inc(i)
 
+iterator mitems*[IX, T](a: var array[IX, T]): var T {.inline.} =
+  ## iterates over each item of `a` so that you can modify the yielded value.
+  var i = low(IX)
+  if i <= high(IX):
+    while true:
+      yield a[i]
+      if i >= high(IX): break
+      inc(i)
+
 iterator items*[T](a: set[T]): T {.inline.} =
   ## iterates over each element of `a`. `items` iterates only over the
   ## elements that are really in the set (and not over the ones the set is
@@ -1680,6 +1696,13 @@ iterator items*(a: cstring): char {.inline.} =
     yield a[i]
     inc(i)
 
+iterator mitems*(a: var cstring): var char {.inline.} =
+  ## iterates over each item of `a` so that you can modify the yielded value.
+  var i = 0
+  while a[i] != '\0':
+    yield a[i]
+    inc(i)
+
 iterator items*(E: typedesc[enum]): E =
   ## iterates over the values of the enum ``E``.
   for v in low(E)..high(E):
@@ -1692,6 +1715,14 @@ iterator pairs*[T](a: openArray[T]): tuple[key: int, val: T] {.inline.} =
     yield (i, a[i])
     inc(i)
 
+iterator mpairs*[T](a: var openArray[T]): tuple[key: int, val: var T] {.inline.} =
+  ## iterates over each item of `a`. Yields ``(index, a[index])`` pairs.
+  ## ``a[index]`` can be modified.
+  var i = 0
+  while i < len(a):
+    yield (i, a[i])
+    inc(i)
+
 iterator pairs*[IX, T](a: array[IX, T]): tuple[key: IX, val: T] {.inline.} =
   ## iterates over each item of `a`. Yields ``(index, a[index])`` pairs.
   var i = low(IX)
@@ -1701,6 +1732,16 @@ iterator pairs*[IX, T](a: array[IX, T]): tuple[key: IX, val: T] {.inline.} =
       if i >= high(IX): break
       inc(i)
 
+iterator mpairs*[IX, T](a: var array[IX, T]): tuple[key: IX, val: var T] {.inline.} =
+  ## iterates over each item of `a`. Yields ``(index, a[index])`` pairs.
+  ## ``a[index]`` can be modified.
+  var i = low(IX)
+  if i <= high(IX):
+    while true:
+      yield (i, a[i])
+      if i >= high(IX): break
+      inc(i)
+
 iterator pairs*[T](a: seq[T]): tuple[key: int, val: T] {.inline.} =
   ## iterates over each item of `a`. Yields ``(index, a[index])`` pairs.
   var i = 0
@@ -1708,6 +1749,14 @@ iterator pairs*[T](a: seq[T]): tuple[key: int, val: T] {.inline.} =
     yield (i, a[i])
     inc(i)
 
+iterator mpairs*[T](a: var seq[T]): tuple[key: int, val: var T] {.inline.} =
+  ## iterates over each item of `a`. Yields ``(index, a[index])`` pairs.
+  ## ``a[index]`` can be modified.
+  var i = 0
+  while i < len(a):
+    yield (i, a[i])
+    inc(i)
+
 iterator pairs*(a: string): tuple[key: int, val: char] {.inline.} =
   ## iterates over each item of `a`. Yields ``(index, a[index])`` pairs.
   var i = 0
@@ -1715,6 +1764,29 @@ iterator pairs*(a: string): tuple[key: int, val: char] {.inline.} =
     yield (i, a[i])
     inc(i)
 
+iterator mpairs*(a: var string): tuple[key: int, val: var char] {.inline.} =
+  ## iterates over each item of `a`. Yields ``(index, a[index])`` pairs.
+  ## ``a[index]`` can be modified.
+  var i = 0
+  while i < len(a):
+    yield (i, a[i])
+    inc(i)
+
+iterator pairs*(a: cstring): tuple[key: int, val: char] {.inline.} =
+  ## iterates over each item of `a`. Yields ``(index, a[index])`` pairs.
+  var i = 0
+  while a[i] != '\0':
+    yield (i, a[i])
+    inc(i)
+
+iterator mpairs*(a: var cstring): tuple[key: int, val: var char] {.inline.} =
+  ## iterates over each item of `a`. Yields ``(index, a[index])`` pairs.
+  ## ``a[index]`` can be modified.
+  var i = 0
+  while a[i] != '\0':
+    yield (i, a[i])
+    inc(i)
+
 
 proc isNil*[T](x: seq[T]): bool {.noSideEffect, magic: "IsNil".}
 proc isNil*[T](x: ref T): bool {.noSideEffect, magic: "IsNil".}
@@ -2992,6 +3064,15 @@ iterator items*[T](a: seq[T]): T {.inline.} =
     inc(i)
     assert(len(a) == L, "seq modified while iterating over it")
 
+iterator mitems*[T](a: var seq[T]): var T {.inline.} =
+  ## iterates over each item of `a` so that you can modify the yielded value.
+  var i = 0
+  let L = len(a)
+  while i < L:
+    yield a[i]
+    inc(i)
+    assert(len(a) == L, "seq modified while iterating over it")
+
 iterator items*(a: string): char {.inline.} =
   ## iterates over each item of `a`.
   var i = 0
@@ -3001,6 +3082,15 @@ iterator items*(a: string): char {.inline.} =
     inc(i)
     assert(len(a) == L, "string modified while iterating over it")
 
+iterator mitems*(a: var string): var char {.inline.} =
+  ## iterates over each item of `a` so that you can modify the yielded value.
+  var i = 0
+  let L = len(a)
+  while i < L:
+    yield a[i]
+    inc(i)
+    assert(len(a) == L, "string modified while iterating over it")
+
 when not defined(nimhygiene):
   {.pragma: inject.}
 
diff --git a/tests/stdlib/tmitems.nim b/tests/stdlib/tmitems.nim
new file mode 100644
index 0000000000..2297f0ee93
--- /dev/null
+++ b/tests/stdlib/tmitems.nim
@@ -0,0 +1,136 @@
+discard """
+  output: '''@[11, 12, 13]
+@[11, 12, 13]
+@[1, 3, 5]
+@[1, 3, 5]
+gppcbs
+gppcbs
+fpqeew
+fpqeew
+[11, 12, 13]
+[11, 12, 13]
+[11, 12, 13]
+[11, 12, 13]
+{ "key1": 11,  "key2": 12,  "key3": 13}
+[ 11,  12,  13]
+<Students>
+  <Student Name="Aprilfoo" />
+  <Student Name="bar" />
+</Students>'''
+"""
+
+block:
+  var xs = @[1,2,3]
+  for x in xs.mitems:
+    x += 10
+  echo xs
+
+block:
+  var xs = [1,2,3]
+  for x in xs.mitems:
+    x += 10
+  echo(@xs)
+
+block:
+  var xs = @[1,2,3]
+  for i, x in xs.mpairs:
+    x += i
+  echo xs
+
+block:
+  var xs = [1,2,3]
+  for i, x in xs.mpairs:
+    x += i
+  echo(@xs)
+
+block:
+  var x = "foobar"
+  for c in x.mitems:
+    inc c
+  echo x
+
+block:
+  var x = "foobar"
+  var y = cast[cstring](addr x[0])
+  for c in y.mitems:
+    inc c
+  echo x
+
+block:
+  var x = "foobar"
+  for i, c in x.mpairs:
+    inc c, i
+  echo x
+
+block:
+  var x = "foobar"
+  var y = cast[cstring](addr x[0])
+  for i, c in y.mpairs:
+    inc c, i
+  echo x
+
+import lists
+
+block:
+  var sl = initSinglyLinkedList[int]()
+  sl.prepend(3)
+  sl.prepend(2)
+  sl.prepend(1)
+  for x in sl.mitems:
+    x += 10
+  echo sl
+
+block:
+  var sl = initDoublyLinkedList[int]()
+  sl.append(1)
+  sl.append(2)
+  sl.append(3)
+  for x in sl.mitems:
+    x += 10
+  echo sl
+
+block:
+  var sl = initDoublyLinkedRing[int]()
+  sl.append(1)
+  sl.append(2)
+  sl.append(3)
+  for x in sl.mitems:
+    x += 10
+  echo sl
+
+import queues
+
+block:
+  var q = initQueue[int]()
+  q.add(1)
+  q.add(2)
+  q.add(3)
+  for x in q.mitems:
+    x += 10
+  echo q
+
+import json
+
+block:
+  var j = parseJson """{"key1": 1, "key2": 2, "key3": 3}"""
+  for key,val in j.pairs:
+    val.num += 10
+  echo j
+
+block:
+  var j = parseJson """[1, 2, 3]"""
+  for x in j.mitems:
+    x.num += 10
+  echo j
+
+import xmltree, xmlparser, streams, strtabs
+
+block:
+  var d = parseXml(newStringStream """<Students>
+    <Student Name="April" Gender="F" DateOfBirth="1989-01-02" />
+    <Student Name="Bob" Gender="M"  DateOfBirth="1990-03-04" />
+  </Students>""")
+  for x in d.mitems:
+    x = <>Student(Name=x.attrs["Name"] & "foo")
+  d.mget(1).attrs["Name"] = "bar"
+  echo d