`andGroup` underdocumented

I wanted to use andGroup and figured, if i would not already have known what it does, how its called and what its usefull for, i would not really have understood that from the docstring or got pointed to it:

• one liner docstring is missleading/uncomprehensive (mostly because notion of field values is somewhat vague/ambigue)
• simple example in the functions description would really help