The Picard documentation describes that the _format metadata variable available to tagger scripts contains the "Media format of the file e.g. MPEG-1 Audio."
Now consider the following tagger script, attempting to use this variable:
If I load an MP3 file into Picard (version 2.3.1), then run the script manually from the "Run Scripts" item in the context menu, this seems to work fine: the tag value is set to "MPEG-1 Layer 3 - ID3v2.4"
However if I check the box in the options menu to automatically run this script, when the file is loaded or the release is refreshed the tag is set to the empty string / removed (and is subseqeuntly restored by manually running the script again).
This seems very strange, I was expecting the script to behave identically when run manually versus automatically...