Fix example in README and docstring around how width actually works

README.md

@@ -13,7 +13,7 @@ birth).  Every day it will choose a new memento randomly and put it into
 `global-mode-string' which is usually displayed in the mode line.  There is also
 an option to show it in the frame title instead of the global-mode-string.
 
-# Installation
+## Installation
 
 Install from [MELPA](https://melpa.org/#/memento-mori).
 
@@ -27,7 +27,7 @@ e.g. If you have something like the following in your emacs config
 ```emacs-lisp
 (require 'memento-mori)
 (setq memento-mori-mementos
-      '(("%.2f years old" :since "1970-01-01")))
+      '(("%.5Y years old" :since "1970-01-01")))
 (memento-mori-mode)
 ```
 
@@ -37,7 +37,7 @@ Or using `use-package`:
 (use-package memento-mori
   :ensure t
   :custom (memento-mori-mementos
-           '(("%.2f years old" :since "1970-01-01")))
+           '(("%.5Y years old" :since "1970-01-01")))
   :config (memento-mori-mode))
 ```
 

memento-mori.el

@@ -51,7 +51,7 @@
   :group 'help)
 
 (defcustom memento-mori-display-in-modeline t
   "If non-nil, `memento-mori-mode' will add mementos to the mode line.
 Really, it adds it to the `global-mode-string', which usually
 appears in the mode line, however, if you have customized your
 mode line it may not appear."
@@ -59,7 +59,7 @@
   :type 'boolean)
 
 (defcustom memento-mori-display-in-frame-title nil
   "If non-nil, `memento-mori-mode' will add mementos to the frame title."
   :group 'memento-mori
   :type 'boolean)
 
@@ -145,12 +145,15 @@
 %F  The result of the `:formula' as a float.
 %%  A literal percent sign.
 
-As shown, most sequences have a upper case and a lower case
-version.  The lower case versions are truncated to integers since
-this is a common use case.  The upper case versions return a
-float for full control, but will likely require a width or
-precision specifier in practice, such as \"%.2Y\" to show the
-number of years with two decimal points of precision."
+As shown, most sequences have a upper case and a lower case version.
+The lower case versions are truncated to integers since this is a common
+use case.  The upper case versions return a float for full control, but
+will likely require a width or precision specifier in practice.
+Unfortunately, the width and precision specifiers behave like the
+corresponding ones in format when applied to %s, so they define the
+width in characters, not the number of decimal places.  Therefore,
+\"%.5Y\" will show the number of years with two or three decimal points
+of precision depending on if it's longer than 10 years or not."
   :group 'memento-mori
   :type '(repeat (cons
                   (string :tag "Format string")
@@ -242,8 +245,8 @@
 (defvar memento-mori-string ""
   "The memento mori memento.
 The string shown in the mode line and/or frame title when
 `memento-mori-mode' is enabled.  This is not meant to be changed
 by the user, but can be used in other places such as org-mode
 agendas to display the current momento.")
 
 (defvar memento-mori--modeline-construct
@@ -275,7 +278,7 @@
     (error "Birth date not set.  Try M-x customize-group memento-mori")))
 
 (defun memento-mori--parse-time (value)
   "Return your birth time in `encode-time' format.
 The birth time is parsed from `memento-mori-birth-date' using
 `parse-time-string'.  An error is signaled if it is not valid."
   (when (symbolp value)
@@ -309,7 +312,7 @@
   "Randomly choose a quote from `memento-mori-quotes'."
   (nth (random (length memento-mori-quotes)) memento-mori-quotes))
 
 (defun memento-mori--format-memento (memento)
   "Format MEMENTO based on the current time."
   (let* ((format-string (car memento))
          (args-plist (cdr memento))
@@ -317,7 +320,7 @@
          (since-value (plist-get args-plist :since))
          (_ (when (not (or until-value since-value))
                  (error ":since or :until required.  Parsing %s" memento)))
          (current-time-list nil)
          (until-seconds (when until-value
                           (float-time
                            (time-subtract
@@ -348,7 +351,7 @@
                                      (/ since-seconds (* 60 60 24))
                                      days))
                            (t 0)))))
     (format-spec format-string
                  `((?Y . ,years)
                    (?y . ,(truncate years))
                    (?M . ,months)
@@ -384,13 +387,13 @@
   (when (and memento-mori-initial-scratch-message
              (boundp 'initial-scratch-message))
     (setq initial-scratch-message
           (format-spec memento-mori-initial-scratch-message
                        `((?m . ,memento-mori-string)
                          (?q . ,(memento-mori--random-quote)))
                        'ignore))))
 
 (defun memento-mori--add-mementos ()
   "Adds constructs to mode line and/or frame title to display `memento-mori-mementos'.
 Where it adds it is controlled by `memento-mori-display-in-modeline' and
 `memento-mori-display-in-frame-title' respectively.