code: public void register(final Field field) {
          Requires requires = field.getAnnotation(Requires.class);
          if (requires != null) {
              final String[] requirements = requires.value();
              for (String requirement: requirements) {
                  this.dependantToRequirementsMap.put(field, requirement);
                  this.requirementToDependantMap.put(requirement, field);
              }
  
          }
      }
docs: Check if field has the {@link org.mapfish.print.parser.Requires} annotation and registers it and its
  requirement.
  
  @param field the field to inspect