Definition of a macro:

• macro definition within a Macro section, following the httpd configuration style.
• user defined names for the macro and its parameters.
• macro names are case-insensitive, like httpd directives.
• macro parameter names are case sensitive.
• macro parameters must have distinct names.
• error on empty parameter names.
• redefining a macro generates a warning.
• macro definitions can be nested... (but what for?)
• warn about unused macro parameters.
• warn about macro parameter names which prefix one another.
• warn if a parameter is not prefixed by any of '$%@' (good practice).
• the available prefixes help deal with interactions with other directives such as Define.
• tip: it may be useful to define a macro parameter with surrounding braces, say ${foo} so that the name can appear with surrounding characters such as bla${foo}bla.
• warn about empty macro contents.
• warns if sections are not properly nested within a macro. (if it is detected so).
• the lexical scope of macro parameters is restricted to the macro text, it is not forwarded to includes for instance.
• arbitrary contents in macros.

  It means you can put perl sections or whatever you like in a macro. No assumption is made about the lexical structure (quotes, spaces or whatever) within the macro contents but to expect a set of backslash-continued independent lines.

Use of a macro:

• number of arguments must match the definition.
• all occurences of macro parameters are substituted by their values.
• in case of conflicts, the longest parameter name is chosen.
• macro expansion recursion is detected and stopped (error).
• warn about empty arguments when used.
• on errors, try to describe precisely where the error occured.
• $ and %-prefixed parameters are not escaped.
• @-prefixed parameters are escaped in quotes.

Removal of a macro definition:

• the macro must be already defined.

A common usage of mod_macro is for the creation of dynamically-generated virtual hosts.