GWT modules may declare one or more `<servlet>` tags. These define Java Servlets that implement the server-side component of a GWT-enabled web application.

Prior to GWT 1.6, these GWT module servlet tags controlled the set of servlets were actually instantiated during hosted mode. But as of GWT 1.6, this is no longer true. Instead, the web application's `WEB-INF/web.xml` configuration file controls what servlets are instantiated. A GWT module specifies only what servlets are expected.

During hosted mode startup, the set of expected servlets (from GWT module `<servlet>` tags) is validated against the set of actual servlets (from the `WEB-INF/web.xml`) and a warning is issued for each expected servlet which does not match an actual servlet.