IfDefinetags surround configuration directives that are applied if the "test" stated in the
IfDefinetag is true. The directives are ignored if the test is false.
IfDefinetags is a parameter name (for example,
HAVE_PERL). If the parameter is defined, meaning that it is provided as an argument to the server's start-up command, then the test is true. In this case, when the Web server is started, the test is true and the directives contained in the
IfDefinetags are applied.