is on the special value of the
hammer as a nut cracker, nail driver, etc.

(15) In those cases where the title is so obvious that definition is
superfluous, explanatory notes may be substituted and will usually be
found helpful.

CROSS-REFERENCES AND SEARCH-NOTES.

(16) Inasmuch as nearly every patent discloses unclaimed matter that is
classifiable separately from the claimed matter, it is clearly
impossible to cross-reference every disclosure of every means in every
patent. Many things must be taken as conventional, obvious, or well
known, and the good judgment of the classifier is bound to be exercised
in cross-referencing matter disclosed but not claimed to be the
invention of the patentee.

(17) A mere part or element should rarely be cross-referenced from an
element class to a superior combination class. An element forming part
of a combination in a superior class should, if claimed, be
cross-referenced to the element class and also if not claimed if it
seems to be not merely a conventional form, and patents having claims
for more than one differently classifiable invention should always be
cross-referenced unless such an arrangement of subclasses with
search-notes is substituted as will guide the searcher to all places
where the material may be found. Claimed matter additional to that which
controls the classification, if belonging in the same class, should be
cross-referenced into a _succeeding_ subclass. Cross-references of
unclaimed disclosure may be in either direction.

(18) To supplement or take the place of cross-referencing, more or less
elaborate search-notes are needed, giving directions and suggestions for
further search, setting out the relationship between classes and
subclasses, and drawing distinctions by example. Search-notes should
indicate other classes or subclasses in which the subject-matter of the
group to which the search-notes are appended is likely to form a part of
a more intensive combination, also analogous matter that might serve as
a reference for a broad claim. They need not, in general, indicate where
parts or elements of the subject-matter which are common also to other
classes can be found, because the index of classes contains the
necessary information. For example, it is not necessary in every
machine-class to indicate by search-notes where machine-elements and
static parts may be found, nor in a class of wooden boxes to point out
where the nails, screws, hinges, or l