store properties,
they also contain plug-ins called @q{engravers} that create notation
elements. For example, the @code{Voice} context contains a
-@code{Note_head_engraver} and the @code{Staff} context contains a
+@code{Note_heads_engraver} and the @code{Staff} context contains a
@code{Key_signature_engraver}.
For a full a description of each plug-in, see