As far as i remember, the highlighted part is Message Source, Message Type and Function Code. So basically message source is an indicator which tells which subsytem produced the message and message type indicates the type of that message.
That is only for trained people on advanced troubleshooting. That info is kinda irrelevant for level 2 support. No documentation as far as I know shows this
I saw it only on my training material as well as many others, but never had used it on customer side, only when arguing with G support when they don’t want to raise a ticket or something like that.
Basically X_Y intended to be used for different log analyzing programs.
[n1:n2] intended to be used for solving serious problems like application crashing and mostly by persons knowing URS internals. They point to exact place in URS code where from.message wad printed.