\n * A valid prefix consists of alphanumeric characters and underscores.\n *
\n * Keep in mind that the prefix must be set before the {@link LoopSectionHelper.Factory} is registered, for example before\n * the {@link #addDefaultSectionHelpers()} method is called. In other words, the {@link LoopSectionHelper.Factory} must be\n * re-registered after the prefix is set.\n *\n * @param prefix\n * @return self\n * @see LoopSectionHelper.Factory\n */\n public EngineBuilder iterationMetadataPrefix(String prefix) {\n if (!LoopSectionHelper.Factory.ITERATION_METADATA_PREFIX_NONE.equals(prefix)\n && !LoopSectionHelper.Factory.ITERATION_METADATA_PREFIX_ALIAS_UNDERSCORE.equals(prefix)\n && !LoopSectionHelper.Factory.ITERATION_METADATA_PREFIX_ALIAS_QM.equals(prefix)\n && !Namespaces.NAMESPACE_PATTERN.matcher(prefix).matches()) {\n throw new TemplateException(\"[\" + prefix\n + \"] is not a valid iteration metadata prefix. The value can only consist of alphanumeric characters and underscores.\");\n }\n this.iterationMetadataPrefix = prefix;\n return this;\n }\n\n /**\n * The global rendering timeout.\n *\n * @param value Timeout in milliseconds\n * @return self\n */\n public EngineBuilder timeout(long value) {\n this.timeout = value;\n return this;\n }\n\n /**","sourceCodeStart":288,"sourceCodeEnd":324,"githubUrl":"https://github.com/quarkusio/quarkus/blob/e1c734241f34c7919086ceb4c9262b4a58f6de44/independent-projects/qute/core/src/main/java/io/quarkus/qute/EngineBuilder.java#L288-L324","documentation":"EngineBuilder.iterationMetadataPrefix(String) validates the prefix for loop iteration metadata (e.g. __qmh or alias forms). Only the special constants (none, alias_underscore, alias_qm) or values matching the namespace/alphanumeric-underscore pattern are accepted; otherwise a TemplateException is thrown at build time.","triggerScenarios":"Calling builder.iterationMetadataPrefix(prefix) with an empty string, or one containing characters other than alphanumerics and underscores (e.g. '-', '.', '$').","commonSituations":"Configuring iteration metadata via application.properties (quarkus.qute.iteration-metadata-prefix) with an invalid value like 'it-' or 'my.prefix', then the EngineProducer passes it to the builder.","solutions":["Use one of the accepted constants: \"none\", \"