# ZChild (filter)

A hook on which to hang various properties (such as At and Name) that control the behavior of an overlapping subwindow.

At
  (At, `0.5 0.5`)
  Position, as discussed in Section [sec:atprop] .
Open
  (Boolean, `FALSE`)
  If true, the subwindow is initially visible. Otherwise, it is invisible until opened by user or program action (typically via PopButton or PopMButton). Open subwindows are useful for achieving layouts that cannot be achieved by a hierarchy of HBoxes and VBoxes.

Notes
  In practice, most overlapping subwindows begin with a ZChild with properties. ZChild itself has no interactive behavior or appearance, but because it is a HighlightVBT, it ensures that Buttons and other descendants that also highlight by HighlightVBT don't visually interfere with other overlapping subwindows.
See Also
  ZSplit and ZChassis