- The command @kbd{C-x C-k C-f} (@code{kmacro-set-format}) prompts
-for the format to use when inserting the macro counter. The default
-format is @samp{%d}. If you set the counter format before you define a
-macro, that format is restored before each repetition of the macro.
-Consequently, any changes you make to the macro counter format while
-defining a macro are only active for the rest of the macro.
+ The command @kbd{C-x C-k C-f} (@code{kmacro-set-format}) prompts for
+the format to use when inserting the macro counter. The default
+format is @samp{%d}, which means to insert the number in decimal
+without any padding. You can exit with empty minibuffer to reset the
+format to this default. You can specify any format string that the
+@code{format} function accepts and that makes sense with a single
+integer extra argument (@pxref{Formatting Strings,,, elisp, The Emacs
+Lisp Reference Manual}). Do not put the format string inside double
+quotes when you insert it in the minibuffer.
+
+ If you use this command while no keyboard macro is being defined or
+executed, the new format affects all subsequent macro definitions.
+Existing macros continue to use the format in effect when they were
+defined. If you set the format while defining a keyboard macro, this
+affects the macro being defined from that point on, but it does not
+affect subsequent macros. Execution of the macro will, at each step,
+use the format in effect at that step during its definition. Changes
+to the macro format during execution of a macro, like the
+corresponding changes during its definition, have no effect on
+subsequent macros.
+
+ The format set by @kbd{C-x C-k C-f} does not affect insertion of
+numbers stored in registers.