SiteMesh 3 is a mature Java web-page decoration and layout framework that intercepts HTML responses (via servlet filter or Spring MVC view resolver), extracts content from the response body (title, head, body, meta tags, custom properties), and merges it into one or more decorator templates. It operates both online (as a servlet filter in Jakarta EE containers) and offline (static site generation via command-line, Ant task, or programmatic API). The core library is module `sitemesh` with no servlet runtime dependencies; additional modules provide integration with Spring MVC (`spring-webmvc-sitemesh`) and Spring Boot auto-configuration (`spring-boot-starter-sitemesh`). The architecture is pipeline-based: response buffering → tolerant HTML tokenization (JFlex-based `TagTokenizer`) → rule-based content processing (`CoreHtmlTagRuleBundle`, `DecoratorTagRuleBundle`) → decorator selection (`PathBasedDecoratorSelector`, `MetaTagBasedDecoratorSelector`) → decorator rendering via `<sitemesh:write>` and `<sitemesh:decorate>` tags. The project demonstrates high craftsmanship in several areas: a pluggable tag-rule bundle system (`TagRuleBundle`), an abstract buffering filter pattern (`ContentBufferingFilter`), a memory-efficient character appendable (`CharSequenceList`), and a path-mapping utility (`PathMapper`) generic enough for reuse outside the decoration context. The response interception layer (`HttpServletResponseBuffer`, `RoutablePrintWriter`, `RoutableServletOutputStream`) is a robust pattern for capturing and modifying servlet output. Container-specific workarounds (`ContainerTweaks`, `DispatchMode`) show deep understanding of servlet container quirks. Maintenance is active, with ongoing support for Jakarta EE 11, Spring Boot 4, and multiple servlet containers (Tomcat 8–11, Jetty 9–12). However, there is technical drift: the Javadoc at `docs/javadoc/3.1.x/` is outdated (Servlet 3–4 era), some configuration documentation references old snapshots, and the build system has configuration-cache workarounds. The project uses a multi-module Gradle setup with examples for Spring Boot, Micronaut, Javalin, and Struts, and includes performance benchmarks. Overall, it is a well-engineered library with a clear separation of concerns, suitable for reuse or extension.