ListGroup : object
In most cases, when a group displays a list of the items in the group as a sublist, it will not want to use the same lister that was used to show the enclosing group, because the enclosing lister will usually have different prefix/suffix styles than the sublist. However, the group list and the enclosing list might share many other attributes, such as the style of name to use when displaying items in the list. The default sublister we create, GroupSublister, is a hybrid that uses the enclosing lister's attributes except for a few, such as the prefix and suffix, that usually need to be changed for the sublist.
This can be overridden to use a completely customized Lister object for the group list, if desired.
For languages (like English) that grammatically distinguish number only between singular and plural, it is sufficient for this to return 1 for singular and anything higher for plural. For the sake of languages that make more elaborate number distinctions for grammatical agreement, though, this should return as accurate a count as is possible.
By default, we return the number of items to be displayed in the list group. This should be overridden when necessary, such as when the group message is singular in usage even if the list has multiple items (as in "$1.38 in change").
By default, we simply return the number of items in the group, since most groups individually list their items.
Note that the same customization could be accomplished by creating a specialized subclass of GroupSublister in createGroupSublister(), and overriding showListItem() in the specialized GroupSublister subclass. We use this mechanism as a convenience, so that a separate group sublister class doesn't have to be created simply to customize the display of group items.
'options', 'indent', and 'infoTab' have the same meaning as they do for showList().
Note that we are not to display any separator before or after our list; the caller is responsible for that.