I was about to write "they look like they should", i.e. for instance in relevant lines
extensions.cfg
Code:
epub:@EPUB_file:1:handleacsm.app,koreader.app,eink-reader.app:ICON_EPUB
handlers.cfg:
Code:
/mnt/ext1/Digital Editions/Lucifero.epub:eink-reader.app
/mnt/ext1/Digital Editions/Malinverno.epub:handleacsm.app
Then I thought I understood what it was: my script (handleacsm.app) was in
/mnt/ext1/applications/ which is
not in $PATH, and it worked from command line only when I was calling it with its full path. I tried then to copy it in
/mnt/secure/bin/ (which is in $PATH), but at no avail.
Finally it occurred to me that
koreader.app is, instead, in
/mnt/ext1/system/bin. And once the script is moved there it works as a handler...
From that I could speculate that the mechanism of adding additional handlers has something going on behind the scenes (for instance in the long-press pulldown menu the label "PB reader" is shown for eink-reader.app, but "koreader.app" and my "handleacsm.app" are shown with their filename), but whatever, I think I have now a first lead.