Sets whether multiple files can be selected in the file chooser.
This is only relevant if the action is set to be %GTK_FILE_CHOOSER_ACTION_OPEN or %GTK_FILE_CHOOSER_ACTION_SELECT_FOLDER.
%TRUE if multiple files can be selected.
See Implementation
Sets whether multiple files can be selected in the file chooser.
This is only relevant if the action is set to be %GTK_FILE_CHOOSER_ACTION_OPEN or %GTK_FILE_CHOOSER_ACTION_SELECT_FOLDER.