/** Returns a filter array with only objects of a specific kind of class.
    An empty array is returned if none found. */
- (NSArray *)dlr_filteredArrayWithKindOfClass:(Class)aClass;

/** Returns the object located after specificed object.
    If last object, returns first object. */
- (id)dlr_objectAfterObject:(id)object;

/** Returns the object located before specificed object.
    If first object, returns last object. */
- (id)dlr_objectBeforeObject:(id)object;

/** Returns true if the array contains an instance of the specified class or its
    subclasses. */
- (BOOL)dlr_containsKindOfClass:(Class)aClass;

/** Returns true if the array contains a member of the specified class. */
- (BOOL)dlr_containsMemberOfClass:(Class)aClass;

/** Returns a string by trimming all of the leading and trailing whitespace characters.
If the receiver is composed entirely of whitespace characters, an empty string is returned. */
- (NSString *)dlr_stringByTrimmingWhitespaceCharacters;

/** If the receiver has a lenght of zero, nil is returned.  Otherwise the receiver is returned. */
- (NSString *)dlr_nilIfEmpty;