System tags can be grouped into two categories:
Tags that can be added to a post
- for:<groupname> copies a post to a group's collection with the tag replaced by from:YourUserName. The copied post will remain unaltered if you change or delete your own post. You must be a member of the group you forward the post to.
Tags that can be used as a filter for search queries
- sys:author:<authorname> filters the search range by author.
- sys:bibtexkey:<bibtexkey> filters the search range by bibtexkey.
- sys:group:<group> filters the search range by group.
- sys:title:<title> filters the search range by title.
- sys:user:<user> filters the search range by user.
I hope this overview will help to improve your experience with BibSonomy.