code: public DocServiceBuilder include(DocServiceFilter filter) {
          requireNonNull(filter, "filter");
          if (includeFilter == ALL_SERVICES) {
              includeFilter = filter;
          } else {
              includeFilter = includeFilter.or(filter);
          }
          return this;
      }
docs: Adds the {@link DocServiceFilter} that checks whether a method will be <b>included</b> while building
  {@link DocService}. The {@link DocServiceFilter} will be invoked with the plugin, service and
  method name. The rule is as follows:
  <ul>
  <li>No {@link #include(DocServiceFilter)} and {@link #exclude(DocServiceFilter)} is called -
  include all methods.</li>
  <li>Only {@link #exclude(DocServiceFilter)} is called -
  include all methods except the methods which the exclusion filter returns {@code true}.</li>
  <li>Only {@link #include(DocServiceFilter)} is called -
  include the methods which the inclusion filter returns {@code true}.</li>
  <li>{@link #include(DocServiceFilter)} and {@link #exclude(DocServiceFilter)} is called -
  include the methods which the inclusion filter returns {@code true} and the exclusion filter
  returns {@code false}.</li>
  </ul>
  
  <P>Note that this can be called multiple times and the {@link DocServiceFilter}s are composed using
  {@link DocServiceFilter#or(DocServiceFilter)} and {@link DocServiceFilter#and(DocServiceFilter)}.
  
  @see #exclude(DocServiceFilter)
  @see DocService to find out how DocService generates documentaion