Caudium is based on Roxen 1.3, even if we have added some new modules types in 1.2 and in 1.3 version of Caudium, the following figure can help you on how modules are called on Caudium.

The Caudium Cache by James Tyson (for Caudium 1.3)

• A MODULE_PARSER that is a container. A container is an HTML structure that may have attributes as well as contents within a tag. The <a> tag is a container as it has information within the tag and its closing tag.
• A MODULE_PARSER This type of module will define an HTML tag that may have parameters, but will not have a closing tag. An example of this is the <br /> tag. While <br /> doesn't take arguments, the MODULE_PARSER can act on arguments passed to it.
• A MODULE_LAST This module will usually deal with a request after every other module in the server configuration has failed to handle the current request. Typically this module type would be used to deal with an Error condition.
• A MODULE_FIRST This will allow you to do some preprocessing on each request that comes in. You can look at the referrer and make a determination of whether to parse the page a certain way. You can look at many other aspects of the connection request and set variables that can be accessed from other modules. The GSession and 123Session Modules both use a MODULE_FIRST to handle incoming requests.
• A MODULE_LOCATION, a more conventional type
• A MODULE_URL template
• An Authorization Module template
• A MODULE_LOGGER example and tutorial.
• Finally a little tip on howto avoid recursive container parsing