Group items in iApp multichoice selection field

The bold header in choice and multichoice fields was meant to categorize file names by folder, but not really meant as a user feature. Nevertheless, if you prefix each value in your list with the desired header text encased in slash characters, the result will be show the header in bold.

choice abc tcl {
    return "/header/item1\n/header/item2\n/header/item3"
}