Application Log - Use of Sortfield ALSORT

My customer wants to filter application log messages by special criteria added when storing the message using function BAL_LOG_MSG_ADD.

We populated the 3-character Field ALSORT, When we display the log in SLG1, ALSORT is always empty.

I'm not quite sure about the use of the ALSORT field - probably it may have been used in outdated versions of Application Log functions.

Any idea about how to populate and use the field ALSORT (hidden in standard ALV dieplay in SLG1). Or a bettter idea about grouping/filtering the log?

Thank you

Clemens