В ассистанте сказано лишь это:
You can also specify the form's Include Hints; i.e. provide a list of the header files which then will be included in the form window's associated .ui file. Header files may be local, i.e. relative to the project's directory, "mywidget.h", or global, i.e. part of Qt or the compilers standard libraries: <QtGui/QWidget>.
Finally, you can specify the function used to load pixmaps into the form window (the Pixmap Function).
Реальноя никогда не использовал эти фичи
