Macros are defined using Macro blocks, which contain the portion of your configuration that needs to be repeated, complete with variables for those parts that will need to be substituted.

For example, you might use a macro to define a VirtualHost block, in order to define multiple similar virtual hosts:

Macro names are case-insensitive, like httpd configuration directives. However, variable names are case sensitive.

You would then invoke this macro several times to create virtual hosts:

At server startup time, each of these Use invocations would be expanded into a full virtualhost, as described by the Macro definition.

The UndefMacro directive is used so that later macros using the same variable names don't result in conflicting definitions.

A more elaborate version of this example may be seen below in the Examples section.

Parameter names should begin with a sigil such as $, %, or @, so that they are clearly identifiable, and also in order to help deal with interactions with other directives, such as the core Define directive. Failure to do so will result in a warning. Nevertheless, you are encouraged to have a good knowledge of your entire server configuration in order to avoid reusing the same variables in different scopes, which can cause confusion.

Parameters prefixed with either $ or % are not escaped. Parameters prefixes with @ are escaped in quotes.

Avoid using a parameter which contains another parameter as a prefix, (For example, $win and $winter) as this may cause confusion at expression evaluation time. In the event of such confusion, the longest possible parameter name is used.

If you want to use a value within another string, it is useful to surround the parameter in braces, to avoid confusion: