The Entries[Enable] command enables an entry to be displayed in the context menu.  If a selected object satisfies the criteria for this entry's display, the entry will appear in a context menu.

The parameter action specifies the action or actions to enable. If action is a string, any entry in the top-level context menu with this name will be enabled.  If action is a list of strings, this is interpreted as a hierarchical sequence of submenus starting from the top-level menu.  Any menu entries whose submenu entry sequence begins with action will be enabled.

with(ContextMenu[CurrentContext]):

Enable the top-level menu entry that negates a boolean value.

Entries[Enable]("Negate");

Enable the submenu entry that sorts a list in ascending order.

Entries[Enable](["Sorts", "Ascending Order"]);