gh-122767: document "new style" formatting for complexes

Doc/library/string.rst

@@ -350,8 +350,9 @@ The meaning of the various alignment options is as follows:
 | ``'='`` | Forces the padding to be placed after the sign (if any)  |
 |         | but before the digits.  This is used for printing fields |
 |         | in the form '+000000120'. This alignment option is only  |
-|         | valid for numeric types.  It becomes the default for     |
-|         | numbers when '0' immediately precedes the field width.   |
+|         | valid for numeric types, excluding :class:`complex`.     |
+|         | It becomes the default for numbers when '0' immediately  |
+|         | precedes the field width.                                |
 +---------+----------------------------------------------------------+
 | ``'^'`` | Forces the field to be centered within the available     |
 |         | space.                                                   |
@@ -432,9 +433,9 @@ including any prefixes, separators, and other formatting characters.
 If not specified, then the field width will be determined by the content.
 
 When no explicit alignment is given, preceding the *width* field by a zero
-(``'0'``) character enables
-sign-aware zero-padding for numeric types.  This is equivalent to a *fill*
-character of ``'0'`` with an *alignment* type of ``'='``.
+(``'0'``) character enables sign-aware zero-padding for numeric types,
+excluding :class:`complex`.  This is equivalent to a *fill* character of
+``'0'`` with an *alignment* type of ``'='``.
 
 .. versionchanged:: 3.10
    Preceding the *width* field by ``'0'`` no longer affects the default
@@ -588,6 +589,14 @@ The available presentation types for :class:`float` and
    |         | as altered by the other format modifiers.                |
    +---------+----------------------------------------------------------+
 
+The available presentation types for :class:`complex` are same as for
+:class:`float`.  Both real and imaginary components of a complex number are
+formatted as floating-point numbers, accordingly specified presentaion type.
+They separated by mandatory sign of the imaginary part, terminated by ``j``
+suffix.  If presentation type is missing --- result match the output of
+:func:`str` (numbers also surrounded by round parentheses, if real part is
+non-zero), altered by other format modifiers.
+
 
 .. _formatexamples: