diff --git a/lib/pure/parseutils.nim b/lib/pure/parseutils.nim
index 31598f8c6f..3545d1fcdc 100644
--- a/lib/pure/parseutils.nim
+++ b/lib/pure/parseutils.nim
@@ -56,10 +56,12 @@ const
   IdentStartChars = {'a'..'z', 'A'..'Z', '_'}
     ## copied from strutils
 
+template toOa(s: string, start: int): openArray[char] = s.toOpenArray(start, s.high)
+
 proc toLower(c: char): char {.inline.} =
   result = if c in {'A'..'Z'}: chr(ord(c)-ord('A')+ord('a')) else: c
 
-proc parseBin*[T: SomeInteger](s: string, number: var T, start = 0,
+proc parseBin*[T: SomeInteger](s: openArray[char], number: var T,
     maxLen = 0): int {.noSideEffect.} =
   ## Parses a binary number and stores its value in ``number``.
   ##
@@ -67,8 +69,8 @@ proc parseBin*[T: SomeInteger](s: string, number: var T, start = 0,
   ## If error, the value of ``number`` is not changed.
   ##
   ## If ``maxLen == 0``, the parsing continues until the first non-bin character
-  ## or to the end of the string. Otherwise, no more than ``maxLen`` characters
-  ## are parsed starting from the ``start`` position.
+  ## or to the end of the array. Otherwise, no more than ``maxLen`` characters
+  ## are from the array.
   ##
   ## It does not check for overflow. If the value represented by the string is
   ## too big to fit into ``number``, only the value of last fitting characters
@@ -89,7 +91,7 @@ proc parseBin*[T: SomeInteger](s: string, number: var T, start = 0,
     var num64: int64
     doAssert parseBin("0100111001101001111011010100111001101001", num64) == 40
     doAssert num64 == 336784608873
-  var i = start
+  var i = 0
   var output = T(0)
   var foundDigit = false
   let last = min(s.len, if maxLen == 0: s.len else: i + maxLen)
@@ -104,9 +106,19 @@ proc parseBin*[T: SomeInteger](s: string, number: var T, start = 0,
     inc(i)
   if foundDigit:
     number = output
-    result = i - start
+    result = i
 
-proc parseOct*[T: SomeInteger](s: string, number: var T, start = 0,
+proc parseBin*[T: SomeInteger](s: string, number: var T, start = 0,
+    maxLen = 0): int {.noSideEffect.} =
+  ## `string` overload of `parseBin`_
+  ## If ``maxLen == 0``, the parsing continues until the first non-bin character
+  ## or to the end of the string. Otherwise, no more than ``maxLen`` characters
+  ## are parsed starting from the ``start`` position.
+  ## see `parseBin` for further docs
+  s.toOa(start).parseBin(number, maxLen)
+
+
+proc parseOct*[T: SomeInteger](s: openArray[char], number: var T,
     maxLen = 0): int {.noSideEffect.} =
   ## Parses an octal number and stores its value in ``number``.
   ##
@@ -115,7 +127,7 @@ proc parseOct*[T: SomeInteger](s: string, number: var T, start = 0,
   ##
   ## If ``maxLen == 0``, the parsing continues until the first non-oct character
   ## or to the end of the string. Otherwise, no more than ``maxLen`` characters
-  ## are parsed starting from the ``start`` position.
+  ## are from the array.
   ##
   ## It does not check for overflow. If the value represented by the string is
   ## too big to fit into ``number``, only the value of last fitting characters
@@ -136,7 +148,7 @@ proc parseOct*[T: SomeInteger](s: string, number: var T, start = 0,
     var num64: int64
     doAssert parseOct("2346475523464755", num64) == 16
     doAssert num64 == 86216859871725
-  var i = start
+  var i = 0
   var output = T(0)
   var foundDigit = false
   let last = min(s.len, if maxLen == 0: s.len else: i + maxLen)
@@ -151,9 +163,18 @@ proc parseOct*[T: SomeInteger](s: string, number: var T, start = 0,
     inc(i)
   if foundDigit:
     number = output
-    result = i - start
+    result = i
 
-proc parseHex*[T: SomeInteger](s: string, number: var T, start = 0,
+proc parseOct*[T: SomeInteger](s: string, number: var T, start = 0,
+    maxLen = 0): int {.noSideEffect.} =
+  ## `string` overload of `parseOct`_
+  ## If ``maxLen == 0``, the parsing continues until the first non-oct character
+  ## or to the end of the string. Otherwise, no more than ``maxLen`` characters
+  ## are parsed starting from the ``start`` position.
+  s.toOa(start).parseOct(number, maxLen)
+
+
+proc parseHex*[T: SomeInteger](s: openArray[char], number: var T,
     maxLen = 0): int {.noSideEffect.} =
   ## Parses a hexadecimal number and stores its value in ``number``.
   ##
@@ -184,7 +205,7 @@ proc parseHex*[T: SomeInteger](s: string, number: var T, start = 0,
     var num64: int64
     doAssert parseHex("4E69ED4E69ED", num64) == 12
     doAssert num64 == 86216859871725
-  var i = start
+  var i = 0
   var output = T(0)
   var foundDigit = false
   let last = min(s.len, if maxLen == 0: s.len else: i + maxLen)
@@ -206,9 +227,17 @@ proc parseHex*[T: SomeInteger](s: string, number: var T, start = 0,
     inc(i)
   if foundDigit:
     number = output
-    result = i - start
+    result = i
 
-proc parseIdent*(s: string, ident: var string, start = 0): int =
+proc parseHex*[T: SomeInteger](s: string, number: var T, start = 0,
+    maxLen = 0): int {.noSideEffect.} =
+  ## `string` overload of `parseHex`_
+  ## If ``maxLen == 0``, the parsing continues until the first non-hex character
+  ## or to the end of the string. Otherwise, no more than ``maxLen`` characters
+  ## are parsed starting from the ``start`` position.
+  s.toOa(start).parseHex(number, maxLen)
+
+proc parseIdent*(s: openArray[char], ident: var string): int =
   ## Parses an identifier and stores it in ``ident``. Returns
   ## the number of the parsed characters or 0 in case of an error.
   ## If error, the value of `ident` is not changed.
@@ -220,14 +249,19 @@ proc parseIdent*(s: string, ident: var string, start = 0): int =
     doAssert res == "ello"
     doAssert parseIdent("Hello World", res, 6) == 5
     doAssert res == "World"
-  var i = start
+  var i = 0
   if i < s.len and s[i] in IdentStartChars:
     inc(i)
     while i < s.len and s[i] in IdentChars: inc(i)
-    ident = substr(s, start, i-1)
-    result = i-start
+    ident = substr(s, 0, i-1)
+    result = i
 
-proc parseIdent*(s: string, start = 0): string =
+proc parseIdent*(s: string, ident: var string, start = 0): int =
+  ## `string` overload of `parseIdent`_
+  s.toOa(start).parseIdent(ident)
+
+
+proc parseIdent*(s: openArray[char]): string =
   ## Parses an identifier and returns it or an empty string in
   ## case of an error.
   runnableExamples:
@@ -236,13 +270,17 @@ proc parseIdent*(s: string, start = 0): string =
     doAssert parseIdent("Hello World", 5) == ""
     doAssert parseIdent("Hello World", 6) == "World"
   result = ""
-  var i = start
+  var i = 0
   if i < s.len and s[i] in IdentStartChars:
     inc(i)
     while i < s.len and s[i] in IdentChars: inc(i)
-    result = substr(s, start, i-1)
+    result = substr(s, 0, i-1)
 
-proc parseChar*(s: string, c: var char, start = 0): int =
+proc parseIdent*(s: string, start = 0): string =
+  ## `string` overload of `parseIdent`_
+  s.toOa(start).parseIdent()
+
+proc parseChar*(s: openArray[char], c: var char): int =
   ## Parses a single character, stores it in `c` and returns 1.
   ## In case of error (if start >= s.len) it returns 0
   ## and the value of `c` is unchanged.
@@ -252,12 +290,17 @@ proc parseChar*(s: string, c: var char, start = 0): int =
     doAssert c == '\0'
     doAssert "nim".parseChar(c, 0) == 1
     doAssert c == 'n'
-  if start < s.len:
-    c = s[start]
+  if 0 < s.len:
+    c = s[0]
     result = 1
 
-proc skipWhitespace*(s: string, start = 0): int {.inline.} =
-  ## Skips the whitespace starting at ``s[start]``. Returns the number of
+proc parseChar*(s: string, c: var char, start = 0): int =
+  ## `string` overload of `parseChar`_
+  s.toOa(start).parseChar(c)
+
+
+proc skipWhitespace*(s: openArray[char]): int {.inline.} =
+  ## Skips whitespace at the start of ``s``. Returns the number of
   ## skipped characters.
   runnableExamples:
     doAssert skipWhitespace("Hello World", 0) == 0
@@ -265,11 +308,15 @@ proc skipWhitespace*(s: string, start = 0): int {.inline.} =
     doAssert skipWhitespace("Hello World", 5) == 1
     doAssert skipWhitespace("Hello  World", 5) == 2
   result = 0
-  while start+result < s.len and s[start+result] in Whitespace: inc(result)
+  while result < s.len and s[result] in Whitespace: inc(result)
 
-proc skip*(s, token: string, start = 0): int {.inline.} =
-  ## Skips the `token` starting at ``s[start]``. Returns the length of `token`
-  ## or 0 if there was no `token` at ``s[start]``.
+proc skipWhitespace*(s: string, start = 0): int {.inline.} =
+  ## `string` overload of `skipWhitespace`_
+  s.toOa(start).skipWhitespace()
+
+proc skip*(s, token: openArray[char]): int {.inline.} =
+  ## Skips the `token` starting ``s`. Returns the length of `token`
+  ## or 0 if there was no `token` at the start of ``s``.
   runnableExamples:
     doAssert skip("2019-01-22", "2019", 0) == 4
     doAssert skip("2019-01-22", "19", 0) == 0
@@ -277,22 +324,30 @@ proc skip*(s, token: string, start = 0): int {.inline.} =
     doAssert skip("CAPlow", "CAP", 0) == 3
     doAssert skip("CAPlow", "cap", 0) == 0
   result = 0
-  while start+result < s.len and result < token.len and
-      s[result+start] == token[result]:
+  while result < s.len and result < token.len and
+      s[result] == token[result]:
     inc(result)
   if result != token.len: result = 0
 
-proc skipIgnoreCase*(s, token: string, start = 0): int =
+proc skip*(s: string, token: openArray[char], start = 0): int {.inline.} =
+  ## `string` overload of `skip`_
+  s.toOa(start).skip(token)
+
+proc skipIgnoreCase*(s, token: openArray[char]): int =
   ## Same as `skip` but case is ignored for token matching.
   runnableExamples:
     doAssert skipIgnoreCase("CAPlow", "CAP", 0) == 3
     doAssert skipIgnoreCase("CAPlow", "cap", 0) == 3
   result = 0
-  while start+result < s.len and result < token.len and
-      toLower(s[result+start]) == toLower(token[result]): inc(result)
+  while result < s.len and result < token.len and
+      toLower(s[result]) == toLower(token[result]): inc(result)
   if result != token.len: result = 0
 
-proc skipUntil*(s: string, until: set[char], start = 0): int {.inline.} =
+proc skipIgnoreCase*(s: string, token: openArray[char], start = 0): int =
+  ## `string` overload of `skipIgnoreCase`_
+  s.toOa(start).skipIgnoreCase(token)
+
+proc skipUntil*(s: openArray[char], until: set[char]): int {.inline.} =
   ## Skips all characters until one char from the set `until` is found
   ## or the end is reached.
   ## Returns number of characters skipped.
@@ -301,9 +356,14 @@ proc skipUntil*(s: string, until: set[char], start = 0): int {.inline.} =
     doAssert skipUntil("Hello World", {'W'}, 0) == 6
     doAssert skipUntil("Hello World", {'W', 'd'}, 0) == 6
   result = 0
-  while start+result < s.len and s[result+start] notin until: inc(result)
+  while result < s.len and s[result] notin until: inc(result)
 
-proc skipUntil*(s: string, until: char, start = 0): int {.inline.} =
+proc skipUntil*(s: string, until: set[char], start = 0): int {.inline.} =
+  ## `string` overload of `skipUntil`_
+  s.toOa(start).skipUntil(until)
+
+
+proc skipUntil*(s: openArray[char], until: char): int {.inline.} =
   ## Skips all characters until the char `until` is found
   ## or the end is reached.
   ## Returns number of characters skipped.
@@ -313,9 +373,14 @@ proc skipUntil*(s: string, until: char, start = 0): int {.inline.} =
     doAssert skipUntil("Hello World", 'W', 0) == 6
     doAssert skipUntil("Hello World", 'w', 0) == 11
   result = 0
-  while start+result < s.len and s[result+start] != until: inc(result)
+  while result < s.len and s[result] != until: inc(result)
 
-proc skipWhile*(s: string, toSkip: set[char], start = 0): int {.inline.} =
+proc skipUntil*(s: string, until: char, start = 0): int {.inline.} =
+  ## `string` overload of `skipUntil`_
+  s.toOa(start).skipUntil(until)
+
+
+proc skipWhile*(s: openArray[char], toSkip: set[char]): int {.inline.} =
   ## Skips all characters while one char from the set `token` is found.
   ## Returns number of characters skipped.
   runnableExamples:
@@ -323,14 +388,21 @@ proc skipWhile*(s: string, toSkip: set[char], start = 0): int {.inline.} =
     doAssert skipWhile("Hello World", {'e'}) == 0
     doAssert skipWhile("Hello World", {'W', 'o', 'r'}, 6) == 3
   result = 0
-  while start+result < s.len and s[result+start] in toSkip: inc(result)
+  while result < s.len and s[result] in toSkip: inc(result)
 
-proc fastSubstr(s: string; token: var string; start, length: int) =
+proc skipWhile*(s: string, toSkip: set[char], start = 0): int {.inline.} =
+  ## `string` overload of `skipWhile`_
+  s.toOa(start).skipWhile(toSkip)
+
+proc fastSubstr(s: openArray[char]; token: var string; length: int) =
   token.setLen length
-  for i in 0 ..< length: token[i] = s[i+start]
+  for i in 0 ..< length: token[i] = s[i]
 
-proc parseUntil*(s: string, token: var string, until: set[char],
-                 start = 0): int {.inline.} =
+proc fastSubstr(s: string; token: var string; start, length: int) =
+  s.toOa(start).fastSubstr(token, length)
+
+
+proc parseUntil*(s: openArray[char], token: var string, until: set[char]): int {.inline.} =
   ## Parses a token and stores it in ``token``. Returns
   ## the number of the parsed characters or 0 in case of an error. A token
   ## consists of the characters notin `until`.
@@ -342,14 +414,16 @@ proc parseUntil*(s: string, token: var string, until: set[char],
     doAssert myToken == "Hello "
     doAssert parseUntil("Hello World", myToken, {'W', 'r'}, 3) == 3
     doAssert myToken == "lo "
-  var i = start
-  while i < s.len and s[i] notin until: inc(i)
-  result = i-start
-  fastSubstr(s, token, start, result)
+  while result < s.len and s[result] notin until: inc(result)
+  fastSubstr(s, token, result)
   #token = substr(s, start, i-1)
 
-proc parseUntil*(s: string, token: var string, until: char,
+proc parseUntil*(s: string, token: var string, until: set[char],
                  start = 0): int {.inline.} =
+  ## `string` overload of `parseUntil`_
+  s.toOa(start).parseUntil(token, until)
+
+proc parseUntil*(s: openArray[char], token: var string, until: char): int {.inline.} =
   ## Parses a token and stores it in ``token``. Returns
   ## the number of the parsed characters or 0 in case of an error. A token
   ## consists of any character that is not the `until` character.
@@ -361,14 +435,16 @@ proc parseUntil*(s: string, token: var string, until: char,
     doAssert myToken == "Hell"
     doAssert parseUntil("Hello World", myToken, 'o', 2) == 2
     doAssert myToken == "ll"
-  var i = start
-  while i < s.len and s[i] != until: inc(i)
-  result = i-start
-  fastSubstr(s, token, start, result)
+  while result < s.len and s[result] != until: inc result
+  fastSubstr(s, token, result)
   #token = substr(s, start, i-1)
 
-proc parseUntil*(s: string, token: var string, until: string,
+proc parseUntil*(s: string, token: var string, until: char,
                  start = 0): int {.inline.} =
+  ## `string` overload of `parseUntil`_
+  s.toOa(start).parseUntil(token, until)
+
+proc parseUntil*(s: openArray[char], token: var string, until: string): int {.inline.} =
   ## Parses a token and stores it in ``token``. Returns
   ## the number of the parsed characters or 0 in case of an error. A token
   ## consists of any character that comes before the `until`  token.
@@ -378,20 +454,23 @@ proc parseUntil*(s: string, token: var string, until: string,
     doAssert myToken == "Hello "
     doAssert parseUntil("Hello World", myToken, "Wor", 2) == 4
     doAssert myToken == "llo "
-  var i = start
-  while i < s.len:
-    if until.len > 0 and s[i] == until[0]:
+
+  while result < s.len:
+    if until.len > 0 and s[result] == until[0]:
       var u = 1
-      while i+u < s.len and u < until.len and s[i+u] == until[u]:
+      while result+u < s.len and u < until.len and s[result+u] == until[u]:
         inc u
       if u >= until.len: break
-    inc(i)
-  result = i-start
-  fastSubstr(s, token, start, result)
+    inc result
+  fastSubstr(s, token, result)
   #token = substr(s, start, i-1)
 
-proc parseWhile*(s: string, token: var string, validChars: set[char],
+proc parseUntil*(s: string, token: var string, until: string,
                  start = 0): int {.inline.} =
+  ## `string` overload of `parseUntil`_
+  s.toOa(start).parseUntil(token, until)
+
+proc parseWhile*(s: openArray[char], token: var string, validChars: set[char]): int {.inline.} =
   ## Parses a token and stores it in ``token``. Returns
   ## the number of the parsed characters or 0 in case of an error. A token
   ## consists of the characters in `validChars`.
@@ -401,22 +480,30 @@ proc parseWhile*(s: string, token: var string, validChars: set[char],
     doAssert myToken.len() == 0
     doAssert parseWhile("Hello World", myToken, {'W', 'o', 'r'}, 6) == 3
     doAssert myToken == "Wor"
-  var i = start
-  while i < s.len and s[i] in validChars: inc(i)
-  result = i-start
-  fastSubstr(s, token, start, result)
+  while result < s.len and s[result] in validChars: inc result
+  fastSubstr(s, token, result)
   #token = substr(s, start, i-1)
 
-proc captureBetween*(s: string, first: char, second = '\0', start = 0): string =
+proc parseWhile*(s: string, token: var string, validChars: set[char],
+                 start = 0): int {.inline.} =
+  ## `string` overload of `parseWhile`_
+  s.toOa(start).parseWhile(token, validChars)
+
+
+proc captureBetween*(s: openArray[char], first: char, second = '\0'): string =
   ## Finds the first occurrence of ``first``, then returns everything from there
   ## up to ``second`` (if ``second`` is '\0', then ``first`` is used).
   runnableExamples:
     doAssert captureBetween("Hello World", 'e') == "llo World"
     doAssert captureBetween("Hello World", 'e', 'r') == "llo Wo"
     doAssert captureBetween("Hello World", 'l', start = 6) == "d"
-  var i = skipUntil(s, first, start)+1+start
+  var i = skipUntil(s, first)+1
   result = ""
-  discard s.parseUntil(result, if second == '\0': first else: second, i)
+  discard s.toOpenArray(i, s.high).parseUntil(result, if second == '\0': first else: second)
+
+proc captureBetween*(s: string, first: char, second = '\0', start = 0): string =
+  ## `string` overload of `captureBetween`_
+  s.toOa(start).captureBetween(first, second)
 
 proc integerOutOfRangeError() {.noinline.} =
   raise newException(ValueError, "Parsed integer outside of valid range")
@@ -425,10 +512,10 @@ proc integerOutOfRangeError() {.noinline.} =
 when defined(js):
   {.push overflowChecks: off.}
 
-proc rawParseInt(s: string, b: var BiggestInt, start = 0): int =
+proc rawParseInt(s: openArray[char], b: var BiggestInt): int =
   var
     sign: BiggestInt = -1
-    i = start
+    i = 0
   if i < s.len:
     if s[i] == '+': inc(i)
     elif s[i] == '-':
@@ -448,12 +535,12 @@ proc rawParseInt(s: string, b: var BiggestInt, start = 0): int =
       integerOutOfRangeError()
     else:
       b = b * sign
-      result = i - start
+      result = i
 
 when defined(js):
   {.pop.} # overflowChecks: off
 
-proc parseBiggestInt*(s: string, number: var BiggestInt, start = 0): int {.
+proc parseBiggestInt*(s: openArray[char], number: var BiggestInt): int {.
   rtl, extern: "npuParseBiggestInt", noSideEffect, raises: [ValueError].} =
   ## Parses an integer starting at `start` and stores the value into `number`.
   ## Result is the number of processed chars or 0 if there is no integer.
@@ -465,11 +552,14 @@ proc parseBiggestInt*(s: string, number: var BiggestInt, start = 0): int {.
   var res = BiggestInt(0)
   # use 'res' for exception safety (don't write to 'number' in case of an
   # overflow exception):
-  result = rawParseInt(s, res, start)
+  result = rawParseInt(s, res)
   if result != 0:
     number = res
 
-proc parseInt*(s: string, number: var int, start = 0): int {.
+proc parseBiggestInt*(s: string, number: var BiggestInt, start = 0): int {.noSideEffect, raises: [ValueError].} =
+  s.toOa(start).parseBiggestInt(number)
+
+proc parseInt*(s: openArray[char], number: var int): int {.
   rtl, extern: "npuParseInt", noSideEffect, raises: [ValueError].} =
   ## Parses an integer starting at `start` and stores the value into `number`.
   ## Result is the number of processed chars or 0 if there is no integer.
@@ -481,14 +571,18 @@ proc parseInt*(s: string, number: var int, start = 0): int {.
     doAssert parseInt("2019", res, 2) == 2
     doAssert res == 19
   var res = BiggestInt(0)
-  result = parseBiggestInt(s, res, start)
+  result = parseBiggestInt(s, res)
   when sizeof(int) <= 4:
     if res < low(int) or res > high(int):
       integerOutOfRangeError()
   if result != 0:
     number = int(res)
 
-proc parseSaturatedNatural*(s: string, b: var int, start = 0): int {.
+proc parseInt*(s: string, number: var int, start = 0): int =
+  ## `string` overload of `parseInt`_
+  s.toOa(start).parseInt(number)
+
+proc parseSaturatedNatural*(s: openArray[char], b: var int): int {.
     raises: [].} =
   ## Parses a natural number into ``b``. This cannot raise an overflow
   ## error. ``high(int)`` is returned for an overflow.
@@ -498,7 +592,7 @@ proc parseSaturatedNatural*(s: string, b: var int, start = 0): int {.
     var res = 0
     discard parseSaturatedNatural("848", res)
     doAssert res == 848
-  var i = start
+  var i = 0
   if i < s.len and s[i] == '+': inc(i)
   if i < s.len and s[i] in {'0'..'9'}:
     b = 0
@@ -510,13 +604,18 @@ proc parseSaturatedNatural*(s: string, b: var int, start = 0): int {.
         b = high(int)
       inc(i)
       while i < s.len and s[i] == '_': inc(i) # underscores are allowed and ignored
-    result = i - start
+    result = i
 
-proc rawParseUInt(s: string, b: var BiggestUInt, start = 0): int =
+proc parseSaturatedNatural*(s: string, b: var int, start = 0): int {.
+    raises: [].} =
+  ## `string` overload
+  s.toOa(start).parseSaturatedNatural(b)
+
+proc rawParseUInt(s: openArray[char], b: var BiggestUInt): int =
   var
     res = 0.BiggestUInt
     prev = 0.BiggestUInt
-    i = start
+    i = 0
   if i < s.len - 1 and s[i] == '-' and s[i + 1] in {'0'..'9'}:
     integerOutOfRangeError()
   if i < s.len and s[i] == '+': inc(i) # Allow
@@ -530,9 +629,9 @@ proc rawParseUInt(s: string, b: var BiggestUInt, start = 0): int =
       inc(i)
       while i < s.len and s[i] == '_': inc(i) # underscores are allowed and ignored
     b = res
-    result = i - start
+    result = i
 
-proc parseBiggestUInt*(s: string, number: var BiggestUInt, start = 0): int {.
+proc parseBiggestUInt*(s: openArray[char], number: var BiggestUInt): int {.
   rtl, extern: "npuParseBiggestUInt", noSideEffect, raises: [ValueError].} =
   ## Parses an unsigned integer starting at `start` and stores the value
   ## into `number`.
@@ -546,11 +645,15 @@ proc parseBiggestUInt*(s: string, number: var BiggestUInt, start = 0): int {.
   var res = BiggestUInt(0)
   # use 'res' for exception safety (don't write to 'number' in case of an
   # overflow exception):
-  result = rawParseUInt(s, res, start)
+  result = rawParseUInt(s, res)
   if result != 0:
     number = res
 
-proc parseUInt*(s: string, number: var uint, start = 0): int {.
+proc parseBiggestUInt*(s: string, number: var BiggestUInt, start = 0): int =
+  ## `string` overload
+  s.toOa(start).parseBiggestUInt(number)
+
+proc parseUInt*(s: openArray[char], number: var uint): int {.
   rtl, extern: "npuParseUInt", noSideEffect, raises: [ValueError].} =
   ## Parses an unsigned integer starting at `start` and stores the value
   ## into `number`.
@@ -562,20 +665,24 @@ proc parseUInt*(s: string, number: var uint, start = 0): int {.
     doAssert parseUInt("3450", res, 2) == 2
     doAssert res == 50
   var res = BiggestUInt(0)
-  result = parseBiggestUInt(s, res, start)
+  result = parseBiggestUInt(s, res)
   when sizeof(BiggestUInt) > sizeof(uint) and sizeof(uint) <= 4:
     if res > 0xFFFF_FFFF'u64:
       integerOutOfRangeError()
   if result != 0:
     number = uint(res)
 
-proc parseBiggestFloat*(s: string, number: var BiggestFloat, start = 0): int {.
+proc parseUInt*(s: string, number: var uint, start = 0): int =
+  ## `string` overload
+  s.toOa(start).parseUInt(number)
+
+proc parseBiggestFloat*(s: openArray[char], number: var BiggestFloat): int {.
   magic: "ParseBiggestFloat", importc: "nimParseBiggestFloat", noSideEffect.}
   ## Parses a float starting at `start` and stores the value into `number`.
   ## Result is the number of processed chars or 0 if a parsing error
   ## occurred.
 
-proc parseFloat*(s: string, number: var float, start = 0): int {.
+proc parseFloat*(s: openArray[char], number: var float, start = 0): int {.
   rtl, extern: "npuParseFloat", noSideEffect.} =
   ## Parses a float starting at `start` and stores the value into `number`.
   ## Result is the number of processed chars or 0 if there occurred a parsing
@@ -589,10 +696,14 @@ proc parseFloat*(s: string, number: var float, start = 0): int {.
     doAssert parseFloat("32.57", res, 3) == 2
     doAssert res == 57.00
   var bf = BiggestFloat(0.0)
-  result = parseBiggestFloat(s, bf, start)
+  result = parseBiggestFloat(s, bf)
   if result != 0:
     number = bf
 
+proc parseFloat*(s: string, number: var float, start = 0): int =
+  ## `string` overload
+  s.toOa(start).parseFloat(number)
+
 type
   InterpolatedKind* = enum ## Describes for `interpolatedFragments`
                            ## which part of the interpolated string is
@@ -602,9 +713,9 @@ type
     ikVar,                 ## ``var`` part of the interpolated string
     ikExpr                 ## ``expr`` part of the interpolated string
 
-iterator interpolatedFragments*(s: string): tuple[kind: InterpolatedKind,
+iterator interpolatedFragments*(s: openArray[char]): tuple[kind: InterpolatedKind,
   value: string] =
-  ## Tokenizes the string `s` into substrings for interpolation purposes.
+  ## Tokenizes the array `s` into substrings for interpolation purposes.
   ##
   runnableExamples:
     var outp: seq[tuple[kind: InterpolatedKind, value: string]]
diff --git a/lib/system.nim b/lib/system.nim
index 1effd48c5f..5512fc6786 100644
--- a/lib/system.nim
+++ b/lib/system.nim
@@ -2986,7 +2986,7 @@ template once*(body: untyped): untyped =
 
 {.pop.} # warning[GcMem]: off, warning[Uninit]: off
 
-proc substr*(s: string, first, last: int): string =
+proc substr*(s: openArray[char], first, last: int): string =
   ## Copies a slice of `s` into a new string and returns this new
   ## string.
   ##
@@ -3007,7 +3007,7 @@ proc substr*(s: string, first, last: int): string =
   for i in 0 .. L-1:
     result[i] = s[i+first]
 
-proc substr*(s: string, first = 0): string =
+proc substr*(s: openArray[char], first = 0): string =
   result = substr(s, first, high(s))
 
 when defined(nimscript):
diff --git a/lib/system/strmantle.nim b/lib/system/strmantle.nim
index 6644a0d16e..3c5c46a09f 100644
--- a/lib/system/strmantle.nim
+++ b/lib/system/strmantle.nim
@@ -55,8 +55,7 @@ const
 when defined(nimHasInvariant):
   {.push staticBoundChecks: off.}
 
-proc nimParseBiggestFloat(s: string, number: var BiggestFloat,
-                          start = 0): int {.compilerproc.} =
+proc nimParseBiggestFloat(s: openArray[char], number: var BiggestFloat): int {.compilerproc.} =
   # This routine attempt to parse float that can parsed quickly.
   # i.e. whose integer part can fit inside a 53bits integer.
   # their real exponent must also be <= 22. If the float doesn't follow
@@ -65,7 +64,7 @@ proc nimParseBiggestFloat(s: string, number: var BiggestFloat,
   # This avoid the problems of decimal character portability.
   # see: http://www.exploringbinary.com/fast-path-decimal-to-floating-point-conversion/
   var
-    i = start
+    i = 0
     sign = 1.0
     kdigits, fdigits = 0
     exponent = 0
@@ -88,7 +87,7 @@ proc nimParseBiggestFloat(s: string, number: var BiggestFloat,
       if s[i+2] == 'N' or s[i+2] == 'n':
         if i+3 >= s.len or s[i+3] notin IdentChars:
           number = NaN
-          return i+3 - start
+          return i+3
     return 0
 
   # Inf?
@@ -97,7 +96,7 @@ proc nimParseBiggestFloat(s: string, number: var BiggestFloat,
       if s[i+2] == 'F' or s[i+2] == 'f':
         if i+3 >= s.len or s[i+3] notin IdentChars:
           number = Inf*sign
-          return i+3 - start
+          return i+3
     return 0
 
   if i < s.len and s[i] in {'0'..'9'}:
@@ -131,8 +130,8 @@ proc nimParseBiggestFloat(s: string, number: var BiggestFloat,
 
   # if has no digits: return error
   if kdigits + fdigits <= 0 and
-     (i == start or # no char consumed (empty string).
-     (i == start + 1 and hasSign)): # or only '+' or '-
+     (i == 0 or # no char consumed (empty string).
+     (i == 0 + 1 and hasSign)): # or only '+' or '-
     return 0
 
   if i+1 < s.len and s[i] in {'e', 'E'}:
@@ -159,7 +158,7 @@ proc nimParseBiggestFloat(s: string, number: var BiggestFloat,
       number = 0.0*sign
     else:
       number = Inf*sign
-    return i - start
+    return i
 
   # if integer is representable in 53 bits:  fast path
   # max fast path integer is  1<<53 - 1 or  8999999999999999 (16 digits)
@@ -171,14 +170,14 @@ proc nimParseBiggestFloat(s: string, number: var BiggestFloat,
         number = sign * integer.float / powtens[absExponent]
       else:
         number = sign * integer.float * powtens[absExponent]
-      return i - start
+      return i
 
     # if exponent is greater try to fit extra exponent above 22 by multiplying
     # integer part is there is space left.
     let slop = 15 - kdigits - fdigits
     if absExponent <= 22 + slop and not expNegative:
       number = sign * integer.float * powtens[slop] * powtens[absExponent-slop]
-      return i - start
+      return i
 
   # if failed: slow path with strtod.
   var t: array[500, char] # flaviu says: 325 is the longest reasonable literal
@@ -186,8 +185,8 @@ proc nimParseBiggestFloat(s: string, number: var BiggestFloat,
   let maxlen = t.high - "e+000".len # reserve enough space for exponent
 
   let endPos = i
-  result = endPos - start
-  i = start
+  result = endPos
+  i = 0
   # re-parse without error checking, any error should be handled by the code above.
   if i < endPos and s[i] == '.': i.inc
   while i < endPos and s[i] in {'0'..'9','+','-'}: