diff --git a/doc/format_specifications.rdoc b/doc/format_specifications.rdoc
index 7157220c08..e589524f27 100644
--- a/doc/format_specifications.rdoc
+++ b/doc/format_specifications.rdoc
@@ -336,3 +336,13 @@ Format +argument+ (<tt>'%'</tt>) as a single percent character:
   sprintf('%d %%', 100) # => "100 %"
 
 Flags do not apply.
+
+=== Reference by Name
+
+For more complex formatting, Ruby supports a reference by name.
+%<name>s style uses format style, but %{name} style doesn't.
+
+Examples:
+
+  sprintf("%<foo>d : %<bar>f", { :foo => 1, :bar => 2 }) # => 1 : 2.000000
+  sprintf("%{foo}f", { :foo => 1 })                      # => "1f"
diff --git a/io.c b/io.c
index 3b092e5dce..0a78e0b200 100644
--- a/io.c
+++ b/io.c
@@ -8220,7 +8220,10 @@ rb_io_init_copy(VALUE dest, VALUE io)
  *    printf(format_string, *objects) -> nil
  *
  *  Formats and writes +objects+ to the stream.
- *  See Kernel#sprintf for formatting details.
+ *
+ *  For details on +format_string+, see
+ *  {Format Specifications}[rdoc-ref:format_specifications.rdoc].
+ *
  */
 
 VALUE
@@ -8232,14 +8235,17 @@ rb_io_printf(int argc, const VALUE *argv, VALUE out)
 
 /*
  *  call-seq:
- *    printf(string, *objects)               -> nil
- *    printf(io, string, *objects) -> nil
+ *    printf(format_string, *objects)               -> nil
+ *    printf(io, format_string, *objects) -> nil
  *
  *  Equivalent to:
  *
- *    io.write(sprintf(string, *objects))
+ *    io.write(sprintf(format_string, *objects))
  *
- *  With the single argument +string+, formats +objects+ into the string,
+ *  For details on +format_string+, see
+ *  {Format Specifications}[rdoc-ref:format_specifications.rdoc].
+ *
+ *  With the single argument +format_string+, formats +objects+ into the string,
  *  then writes the formatted string to $stdout:
  *
  *    printf('%4.4d %10s %2.2f', 24, 24, 24.0)
@@ -8248,7 +8254,7 @@ rb_io_printf(int argc, const VALUE *argv, VALUE out)
  *
  *    0024         24 24.00#
  *
- *  With arguments +io+ and +string, formats +objects+ into the string,
+ *  With arguments +io+ and +format_string+, formats +objects+ into the string,
  *  then writes the formatted string to +io+:
  *
  *    printf($stderr, '%4.4d %10s %2.2f', 24, 24, 24.0)
diff --git a/object.c b/object.c
index 3ccce45297..a07915606c 100644
--- a/object.c
+++ b/object.c
@@ -3856,263 +3856,16 @@ rb_obj_dig(int argc, VALUE *argv, VALUE obj, VALUE notfound)
 
 /*
  *  call-seq:
- *     format(format_string [, arguments...] )   -> string
- *     sprintf(format_string [, arguments...] )  -> string
+ *     sprintf(format_string *objects)  -> string
  *
- *  Returns the string resulting from applying <i>format_string</i> to
- *  any additional arguments.  Within the format string, any characters
- *  other than format sequences are copied to the result.
+ *  Returns the string resulting from formatting +objects+
+ *  into +format_string+.
  *
- *  The syntax of a format sequence is as follows.
+ *  For details on +format_string+, see
+ *  {Format Specifications}[rdoc-ref:format_specifications.rdoc].
  *
- *    %[flags][width][.precision]type
+ *  Kernel#format is an alias for Kernel#sprintf.
  *
- *  A format
- *  sequence consists of a percent sign, followed by optional flags,
- *  width, and precision indicators, then terminated with a field type
- *  character.  The field type controls how the corresponding
- *  <code>sprintf</code> argument is to be interpreted, while the flags
- *  modify that interpretation.
- *
- *  The field type characters are:
- *
- *      Field |  Integer Format
- *      ------+--------------------------------------------------------------
- *        b   | Convert argument as a binary number.
- *            | Negative numbers will be displayed as a two's complement
- *            | prefixed with `..1'.
- *        B   | Equivalent to `b', but uses an uppercase 0B for prefix
- *            | in the alternative format by #.
- *        d   | Convert argument as a decimal number.
- *        i   | Identical to `d'.
- *        o   | Convert argument as an octal number.
- *            | Negative numbers will be displayed as a two's complement
- *            | prefixed with `..7'.
- *        u   | Identical to `d'.
- *        x   | Convert argument as a hexadecimal number.
- *            | Negative numbers will be displayed as a two's complement
- *            | prefixed with `..f' (representing an infinite string of
- *            | leading 'ff's).
- *        X   | Equivalent to `x', but uses uppercase letters.
- *
- *      Field |  Float Format
- *      ------+--------------------------------------------------------------
- *        e   | Convert floating point argument into exponential notation
- *            | with one digit before the decimal point as [-]d.dddddde[+-]dd.
- *            | The precision specifies the number of digits after the decimal
- *            | point (defaulting to six).
- *        E   | Equivalent to `e', but uses an uppercase E to indicate
- *            | the exponent.
- *        f   | Convert floating point argument as [-]ddd.dddddd,
- *            | where the precision specifies the number of digits after
- *            | the decimal point.
- *        g   | Convert a floating point number using exponential form
- *            | if the exponent is less than -4 or greater than or
- *            | equal to the precision, or in dd.dddd form otherwise.
- *            | The precision specifies the number of significant digits.
- *        G   | Equivalent to `g', but use an uppercase `E' in exponent form.
- *        a   | Convert floating point argument as [-]0xh.hhhhp[+-]dd,
- *            | which is consisted from optional sign, "0x", fraction part
- *            | as hexadecimal, "p", and exponential part as decimal.
- *        A   | Equivalent to `a', but use uppercase `X' and `P'.
- *
- *      Field |  Other Format
- *      ------+--------------------------------------------------------------
- *        c   | Argument is the numeric code for a single character or
- *            | a single character string itself.
- *        p   | The valuing of argument.inspect.
- *        s   | Argument is a string to be substituted.  If the format
- *            | sequence contains a precision, at most that many characters
- *            | will be copied.
- *        %   | A percent sign itself will be displayed.  No argument taken.
- *
- *  The flags modifies the behavior of the formats.
- *  The flag characters are:
- *
- *    Flag     | Applies to    | Meaning
- *    ---------+---------------+-----------------------------------------
- *    space    | bBdiouxX      | Leave a space at the start of
- *             | aAeEfgG       | non-negative numbers.
- *             | (numeric fmt) | For `o', `x', `X', `b' and `B', use
- *             |               | a minus sign with absolute value for
- *             |               | negative values.
- *    ---------+---------------+-----------------------------------------
- *    (digit)$ | all           | Specifies the absolute argument number
- *             |               | for this field.  Absolute and relative
- *             |               | argument numbers cannot be mixed in a
- *             |               | sprintf string.
- *    ---------+---------------+-----------------------------------------
- *     #       | bBoxX         | Use an alternative format.
- *             | aAeEfgG       | For the conversions `o', increase the precision
- *             |               | until the first digit will be `0' if
- *             |               | it is not formatted as complements.
- *             |               | For the conversions `x', `X', `b' and `B'
- *             |               | on non-zero, prefix the result with ``0x'',
- *             |               | ``0X'', ``0b'' and ``0B'', respectively.
- *             |               | For `a', `A', `e', `E', `f', `g', and 'G',
- *             |               | force a decimal point to be added,
- *             |               | even if no digits follow.
- *             |               | For `g' and 'G', do not remove trailing zeros.
- *    ---------+---------------+-----------------------------------------
- *    +        | bBdiouxX      | Add a leading plus sign to non-negative
- *             | aAeEfgG       | numbers.
- *             | (numeric fmt) | For `o', `x', `X', `b' and `B', use
- *             |               | a minus sign with absolute value for
- *             |               | negative values.
- *    ---------+---------------+-----------------------------------------
- *    -        | all           | Left-justify the result of this conversion.
- *    ---------+---------------+-----------------------------------------
- *    0 (zero) | bBdiouxX      | Pad with zeros, not spaces.
- *             | aAeEfgG       | For `o', `x', `X', `b' and `B', radix-1
- *             | (numeric fmt) | is used for negative numbers formatted as
- *             |               | complements.
- *    ---------+---------------+-----------------------------------------
- *    *        | all           | Use the next argument as the field width.
- *             |               | If negative, left-justify the result. If the
- *             |               | asterisk is followed by a number and a dollar
- *             |               | sign, use the indicated argument as the width.
- *
- *  Examples of flags:
- *
- *   # `+' and space flag specifies the sign of non-negative numbers.
- *   sprintf("%d", 123)  #=> "123"
- *   sprintf("%+d", 123) #=> "+123"
- *   sprintf("% d", 123) #=> " 123"
- *
- *   # `#' flag for `o' increases number of digits to show `0'.
- *   # `+' and space flag changes format of negative numbers.
- *   sprintf("%o", 123)   #=> "173"
- *   sprintf("%#o", 123)  #=> "0173"
- *   sprintf("%+o", -123) #=> "-173"
- *   sprintf("%o", -123)  #=> "..7605"
- *   sprintf("%#o", -123) #=> "..7605"
- *
- *   # `#' flag for `x' add a prefix `0x' for non-zero numbers.
- *   # `+' and space flag disables complements for negative numbers.
- *   sprintf("%x", 123)   #=> "7b"
- *   sprintf("%#x", 123)  #=> "0x7b"
- *   sprintf("%+x", -123) #=> "-7b"
- *   sprintf("%x", -123)  #=> "..f85"
- *   sprintf("%#x", -123) #=> "0x..f85"
- *   sprintf("%#x", 0)    #=> "0"
- *
- *   # `#' for `X' uses the prefix `0X'.
- *   sprintf("%X", 123)  #=> "7B"
- *   sprintf("%#X", 123) #=> "0X7B"
- *
- *   # `#' flag for `b' add a prefix `0b' for non-zero numbers.
- *   # `+' and space flag disables complements for negative numbers.
- *   sprintf("%b", 123)   #=> "1111011"
- *   sprintf("%#b", 123)  #=> "0b1111011"
- *   sprintf("%+b", -123) #=> "-1111011"
- *   sprintf("%b", -123)  #=> "..10000101"
- *   sprintf("%#b", -123) #=> "0b..10000101"
- *   sprintf("%#b", 0)    #=> "0"
- *
- *   # `#' for `B' uses the prefix `0B'.
- *   sprintf("%B", 123)  #=> "1111011"
- *   sprintf("%#B", 123) #=> "0B1111011"
- *
- *   # `#' for `e' forces to show the decimal point.
- *   sprintf("%.0e", 1)  #=> "1e+00"
- *   sprintf("%#.0e", 1) #=> "1.e+00"
- *
- *   # `#' for `f' forces to show the decimal point.
- *   sprintf("%.0f", 1234)  #=> "1234"
- *   sprintf("%#.0f", 1234) #=> "1234."
- *
- *   # `#' for `g' forces to show the decimal point.
- *   # It also disables stripping lowest zeros.
- *   sprintf("%g", 123.4)   #=> "123.4"
- *   sprintf("%#g", 123.4)  #=> "123.400"
- *   sprintf("%g", 123456)  #=> "123456"
- *   sprintf("%#g", 123456) #=> "123456."
- *
- *  The field width is an optional integer, followed optionally by a
- *  period and a precision.  The width specifies the minimum number of
- *  characters that will be written to the result for this field.
- *
- *  Examples of width:
- *
- *   # padding is done by spaces,       width=20
- *   # 0 or radix-1.             <------------------>
- *   sprintf("%20d", 123)   #=> "                 123"
- *   sprintf("%+20d", 123)  #=> "                +123"
- *   sprintf("%020d", 123)  #=> "00000000000000000123"
- *   sprintf("%+020d", 123) #=> "+0000000000000000123"
- *   sprintf("% 020d", 123) #=> " 0000000000000000123"
- *   sprintf("%-20d", 123)  #=> "123                 "
- *   sprintf("%-+20d", 123) #=> "+123                "
- *   sprintf("%- 20d", 123) #=> " 123                "
- *   sprintf("%020x", -123) #=> "..ffffffffffffffff85"
- *
- *  For
- *  numeric fields, the precision controls the number of decimal places
- *  displayed.  For string fields, the precision determines the maximum
- *  number of characters to be copied from the string.  (Thus, the format
- *  sequence <code>%10.10s</code> will always contribute exactly ten
- *  characters to the result.)
- *
- *  Examples of precisions:
- *
- *   # precision for `d', 'o', 'x' and 'b' is
- *   # minimum number of digits               <------>
- *   sprintf("%20.8d", 123)  #=> "            00000123"
- *   sprintf("%20.8o", 123)  #=> "            00000173"
- *   sprintf("%20.8x", 123)  #=> "            0000007b"
- *   sprintf("%20.8b", 123)  #=> "            01111011"
- *   sprintf("%20.8d", -123) #=> "           -00000123"
- *   sprintf("%20.8o", -123) #=> "            ..777605"
- *   sprintf("%20.8x", -123) #=> "            ..ffff85"
- *   sprintf("%20.8b", -11)  #=> "            ..110101"
- *
- *   # "0x" and "0b" for `#x' and `#b' is not counted for
- *   # precision but "0" for `#o' is counted.  <------>
- *   sprintf("%#20.8d", 123)  #=> "            00000123"
- *   sprintf("%#20.8o", 123)  #=> "            00000173"
- *   sprintf("%#20.8x", 123)  #=> "          0x0000007b"
- *   sprintf("%#20.8b", 123)  #=> "          0b01111011"
- *   sprintf("%#20.8d", -123) #=> "           -00000123"
- *   sprintf("%#20.8o", -123) #=> "            ..777605"
- *   sprintf("%#20.8x", -123) #=> "          0x..ffff85"
- *   sprintf("%#20.8b", -11)  #=> "          0b..110101"
- *
- *   # precision for `e' is number of
- *   # digits after the decimal point           <------>
- *   sprintf("%20.8e", 1234.56789) #=> "      1.23456789e+03"
- *
- *   # precision for `f' is number of
- *   # digits after the decimal point               <------>
- *   sprintf("%20.8f", 1234.56789) #=> "       1234.56789000"
- *
- *   # precision for `g' is number of
- *   # significant digits                          <------->
- *   sprintf("%20.8g", 1234.56789) #=> "           1234.5679"
- *
- *   #                                         <------->
- *   sprintf("%20.8g", 123456789)  #=> "       1.2345679e+08"
- *
- *   # precision for `s' is
- *   # maximum number of characters                    <------>
- *   sprintf("%20.8s", "string test") #=> "            string t"
- *
- *  Examples:
- *
- *     sprintf("%d %04x", 123, 123)               #=> "123 007b"
- *     sprintf("%08b '%4s'", 123, 123)            #=> "01111011 ' 123'"
- *     sprintf("%1$*2$s %2$d %1$s", "hello", 8)   #=> "   hello 8 hello"
- *     sprintf("%1$*2$s %2$d", "hello", -8)       #=> "hello    -8"
- *     sprintf("%+g:% g:%-g", 1.23, 1.23, 1.23)   #=> "+1.23: 1.23:1.23"
- *     sprintf("%u", -123)                        #=> "-123"
- *
- *  For more complex formatting, Ruby supports a reference by name.
- *  %<name>s style uses format style, but %{name} style doesn't.
- *
- *  Examples:
- *    sprintf("%<foo>d : %<bar>f", { :foo => 1, :bar => 2 })
- *      #=> 1 : 2.000000
- *    sprintf("%{foo}f", { :foo => 1 })
- *      # => "1f"
  */
 
 static VALUE