It sounds like you need an MDI window, where the children are opened within the parent window.
Unfortunately, BlitzPlus doesn't support that yet, and although I'm not certain, I don't *think* you can fudge it by making API calls after creating your window(s).
In my opinion, this is one thing that BlitzPlus really does need in order to make good apps. However, the problem (I suspect), is that I don't *think* (again, I don't claim to *know*) that Mac or Linux have quite the same concept of MDI windows - which is likely to discourage Mark from adding support to BlitzPlus for something specific to Windows.
Which all boils down to - You'll have to roll your own I'm afraid.
Unfortunately, BlitzPlus doesn't support that yet, and although I'm not certain, I don't *think* you can fudge it by making API calls after creating your window(s).
In my opinion, this is one thing that BlitzPlus really does need in order to make good apps. However, the problem (I suspect), is that I don't *think* (again, I don't claim to *know*) that Mac or Linux have quite the same concept of MDI windows - which is likely to discourage Mark from adding support to BlitzPlus for something specific to Windows.
Which all boils down to - You'll have to roll your own I'm afraid.