Issue #15660: Further clarify 0 prefix for width specifier in formats.
diff --git a/Doc/library/string.rst b/Doc/library/string.rst
index 5b917d9..1da0c67 100644
--- a/Doc/library/string.rst
+++ b/Doc/library/string.rst
@@ -327,7 +327,8 @@
| ``'='`` | 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. |
+ | | valid for numeric types. It becomes the default when '0'|
+ | | immediately precedes the field width. |
+---------+----------------------------------------------------------+
| ``'^'`` | Forces the field to be centered within the available |
| | space. |
@@ -376,7 +377,8 @@
*width* is a decimal integer defining the minimum field width. If not
specified, then the field width will be determined by the content.
-Preceding the *width* field by a zero (``'0'``) character enables
+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 ``'='``.