New flag BOX_PAR (&h00100000) may be used with BOX_WIN and BOX_SVA/BOX_RSA to automatically make the pop-up panel act as the parent to any controls (including TPRINT statements) created until the box is removed (with BOX_RSA+BOX_WIN+BOX_PAR). You could have done this yourself using MX_AUTOPARENT except that MSBOXX does not return an identifier for the panel; the BOX_PAR option overcomes that issue and automatically issues the necessary MX_AUTOPARENT calls.
Note that with BOX_WIN, the box/panel is a GUI control, and thus you cannot output plain text on top of it; use TPRINT, DPRINT, AUI_CONTROL, and other GUI control generation statements instead of PRINT. Furthermore, with BOX_PAR, since the panel acts like a parent, the cursor position of controls and text to be placed on it must be adjusted to be relative to the box/panel rather than the screen. (The overall effect is similar to using a regular dialog box.)