A code for action for an empty field

What would be a code for an action to put something in a tag field if it is empty? Let's say a single dot?

It should only be executed [putting the dot sign] when there is nothing in a given field or if it has only white spaces and nothing more

$regexp(%yourfieldhere%,^$,.)

That's the regexp way.

Give yourself a little task and learn and see if you can manage to do it with the $ifgreater(a,b,x,y) and %len() functions.

https://docs.mp3tag.de/scripting

There are no empty tag-fields. If they exist, they are not empty. Otherwise they don't exist.

Action "Format value"

TEST <== $if(%TEST%,%TEST%,'.')

DD.20170824.1626.CEST

Yes

And there are no passive radiators. Every radiator is a passive cooling element. And yet some are made, marketed and sold as passive ones; on the account that they should not require a fan mounted on them

A figure of speech

Works, thank you

Works, thank you

Although both of those codes the do not take into consideration a case when [unwantedely] only a pause or pauses are present in a given field; but that can be of course managed with a running prior to them a simple action
$trim(%FIELD-NAME-HERE%)

$regexp(%yourfieldhere%,^$,.)

Will be to like to work for fields that may or may not have whiitespaces, would be.

$regexp(%yourfieldhere%,^\s*$,.)

I think you meant whitespace/s for pauses... :huh:

No. It is not a figure of speech. There is no such tag in the file and therefore it can't be empty.
The tag-sytems is not a the same as a database with empty entries.

If you have no car you don't say: I have an empty car.

Normal filter-expression in MP3Tag therefore for this case is %tag_example% MISSING.