[This is preliminary documentation and subject to change.]
If this bit is set, the dialog periodically calls the installer. If the property changes, it notifies the controls on the dialog. This style can be used if there is a control on the dialog indicating whether you are out of disk space. If the user switches to another application and adds/removes files or otherwise modifies the available disk space, you can quickly catch the change using this style.
0x0000020 = 32