MiMB is very simular to the VTank in game editor. The top is where the rules are (same as VTank). The middle section under the rules is the conditon area. This the left side of the rule window in VTank. The bottom in MiMB is Action area, which is the right side of the Vtank rule window. If you have used VTank editor, it should be very easy to understand.
There are a couple of limitations. First off, in MiMB you can only go 1 table deep. Meaning if you add an Any/All/Not type under an existing Any/All/Not type, you will not be able to edit or add to those. This is possible under VT, but not in MiMB. VTank can have unlimted nesting, but its rarely used beyond nesting 1 table deep. Also you will have to enter landblocks and landcells by hand (you can easily find the info by clicking your character and doing /vt property dump). Finally, embedded nav routes can be done, but you will have to have the route saved as a .nav through VTank. Just select the correct .nav file when creating that action.
