(?:
        ^system()                  # \1 (this is a system)
    |
        \G(\R)?\t                  # \2 (this is our first of this type)
        (?:
            link()                 # \3 (this is a link)
        |
            \t*object()            # \4 (this is a object)
        )
    )
     (?|"([^"]*)"|(.*))            # \5 (system/link/object name)
    (?(1)\R\tpos (\S+) (\S+))      # \6 (x pos), \7 (y pos)
    (?:
        (?:\1|\3)
        (?=
            (?:
                \R?^\t
                (?:
                    link ()        # \8 (we have at least one link)
                |
                ).*
            )*
        )
    )?
    (                              # \9 (this is a link or object)
        \3(?:\R(?=\tlink )|())     # advance to next link in such a way that we'll know when we reach it that it's not the first one, or \10 (this is our last link)
    |
        \4(?:                      # advance to next object in such a way that we'll know when we reach it that it's not the first one
            (?:\R\t.*)*?
            \R(?=\t+object )
        )?
    )?
|
    ^\S.*                          # comment, or top-level thing that's not a system
    (?:\R\t.*)*
|
    \G\R\t.*
|
    ^\R

(?9(?2:,))                         # comma between link/object names
$5                                 # system/link/object name
(?1
    \t$6\t$7                       # system x pos, y pos
    \t                             # tab before links
    (?8:\t)                        # tab before objects, in case of no links
)
(?10\t)                            # tab before objects, after last link