code: public void setUpMainSchema(String schemaUrl, ErrorHandler errorHandler)
              throws SAXException, Exception, SchemaReadException {
          Schema schema = schemaByUrl(schemaUrl, errorHandler);
          if (schemaUrl.contains("html5")) {
              try {
                  assertionSchema = CheckerSchema.ASSERTION_SCH;
              } catch (Exception e) {
                  throw new SchemaReadException(
                          "Failed to retrieve secondary schema.");
              }
              try {
                  langdetectSchema = CheckerSchema.LANGUAGE_DETECTING_CHECKER;
              } catch (Exception e) {
                  throw new SchemaReadException(
                          "Failed to retrieve secondary schema.");
              }
              schema = new DataAttributeDroppingSchemaWrapper(schema);
              schema = new XmlLangAttributeDroppingSchemaWrapper(schema);
              schema = new RoleAttributeFilteringSchemaWrapper(schema);
              schema = new TemplateElementDroppingSchemaWrapper(schema);
              schema = new NamespaceChangingSchemaWrapper(schema);
              this.hasHtml5Schema = true;
              if ("http://s.validator.nu/html5-all.rnc".equals(schemaUrl)) {
                  System.setProperty("nu.validator.schema.rdfa-full", "1");
              } else {
                  System.setProperty("nu.validator.schema.rdfa-full", "0");
              }
          }
          this.mainSchemaUrl = schemaUrl;
          this.mainSchema = schema;
      }
docs: /* *
  Prepares the main RelaxNG schema to use for document validation, by
  retrieving a serialized schema instance from the copies of known
  http://s.validator.nu/* schemas in the local entity cache packaged with
  the validator code and creating a Schema instance from it. Also checks
  for resolution of secondary schemas.
  
  @param schemaUrl an http://s.validator.nu/* URL
  
  @param errorHandler error handler for schema-error reporting
  
  @throws SchemaReadException if retrieval of any schema fails