Recently I was also wondering how to understand ino:explain output of xquery. I didn’t find any documentation. There isn’t any documentation I guess. Where as, x-query ‘explain’ is documented (http://techcommunity.softwareag.com/ecosystem/documentation/crossvision/ins441/xqlref/explain.htm#explain).
What all I found about xquery-explain is that XQuery tool that comes with tamino (can be accessed standalone or via Tamino X-plorer), applies a styelsheet to the raw xml output and presents the result in readable format. It was enough for my purpose, because I just wanted to know whether my query was using index or not. Simple. I don’t know if any deeper information than that could be obtained from the xquery-explain output (even if it was documented).
So… if you happen to find out more about this, please post back the information. I am interested too.