+@cindex tag groups
+@funindex \tagGroup
+While @code{\keepWithTag} is convenient when dealing with
+@emph{one} set of alternatives, the removal of music tagged with
+@emph{unrelated} tags is problematic when using tags for more than
+one purpose. For that reason, @q{tag groups} of related tags can
+be declared:
+
+@example
+\tagGroup #'(violinI violinII viola cello)
+@end example
+
+declares the respective tags as belonging to one tag group.
+
+@example
+\keepWithTag #'violinI @dots{}
+@end example
+
+will then only be concerned with tags from @code{violinI}'s tag
+group: any element of the included music that is tagged with one
+or more of tags from this set but @emph{not} with @code{violinI}
+will get removed.
+
+To any @code{\keepWithTag} command, only tags from the tag groups
+of the tags given in the command are visible.
+
+Tags cannot be members of more than one tag group.
+
+@funindex \pushToTag
+@funindex \appendToTag
+@cindex splice into tagged music
+