Todo. Add a feature request for CUA compliment ranking

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@@ -30,6 +30,35 @@ the Library’s Functionality with Test Driven Development]].
 
 * Features
 
+** TODO Implement priority output compliant with RFC 5545
+:LOGBOOK:
+- State "TODO"       from              [2023-12-25 mån 08:21]
+:END:
+
+The [[https://datatracker.ietf.org/doc/html/rfc5545#section-3.8.1.9][iCalendar standard]] defines the /PRIORITY/ field, with integer value type
+ranging 0--9. It suggests two priority calendar user agents (CUA):
+
+ 1. High > Medium > Low, for (1--4, 5, 6--9) and 0 undefined
+ 2. A1 > A2 > ... > C3, for (1, 2, ..., 9) and 0 undefined
+
+Other values for future use. Note that "[t]his property defines the relative
+priority for a calendar component [... and it] is useful in prioritizing
+multiple action items for a given time period."
+
+Implement a mapping from Rank N' Auto's 0--1 (0--100 %) to RFC 5545. Apply a
+transformation defined as follows:
+
+  \[
+  \hat{x} = \left\lceil  9 \cdot \left( 1 - \frac{x}{x_{max}}
+  \right)\right\rceil
+  \]
+
+which is =ceil(9 * (1 - x / x_max))=
+
+Produce output according to 2: A, B, C for small N and A1, A2, ... otherwise.
+
+For future, comply with a 1 version: High, Medium, Low.
+
 ** TODO Test command line input and output
 :LOGBOOK:
 - State "TODO"       from              [2023-03-28 tis 08:21]