Filename template function %datetime-custom allows customizing 'weekday' but how to use in filename template itself?

[UNIVAC-Colonel-Panic]

The date component 'weekday' is described in Template functions:

%datetime-custom<locale|year|month|day|weekday|hour|minute|second|hour12|time-zone|fractional-seconds-digits|time-zone-name|era|locale-matcher>: the date and time formatted according to the specified locale and options. See below for the list of options. You can pass (space character) as a value to use the default value for an option. You can also omit options at the end of the list. For example, to format the date and time in the US English format with the year, day, and weekday, you can use "%datetime-custom<en-US|numeric| |numeric| |numeric>".

(snip)
weekday: the weekday format (i.e. "narrow", "short", "long")
(snip)

and Mozilla Developer Network: DateTimeFormat constructor documentation.

My goal is to make 'weekday' as part of the filename template, something like:

{date-iso}-{weekday}_at_{hours-locale}-{minutes-locale}-{seconds-locale} %if-empty<{page-title}|No title>.html

I would be using the "short" value for 'weekday' in order to get the three-character day-of-week abbreviation.

Example filename:

2025-06-29-Sun_at_14-09-41 TechCrunch ｜ Startup and Technology News ｜ Updated Release of CP_M (Control Program for Microcomputers) with AI Integration Due by Christmas.html

[gildas-lormeau]

Sorry for the late reply, you're supposed to write %datetime-custom<en-US||||short> to generate the "Sun" string but it was unfortunately buggy. I've fixed the bug, the fix will be available in the next version.