@Override
    protected void adding(Item item) {
        super.adding(item);
        Validator.ensure("Could not add an item of type " + item.getItemType() +
                         ": Equiv can only have word, wordAlternatives, int, exact, or phrase as children",
                         acceptsChildrenOfType(item.getItemType()));
    }
Creates an EQUIV with the given item and a set of alternate words as children.
The new EQUIV will take connectivity, significance and weight from the given item.

@param item will be modified and added as a child
@param words set of words to create WordItems from
container-search/src/main/java/com/yahoo/prelude/query/EquivItem.java