mod_perl 2.0 provides two backward-compatibility layers: one for the configuration files and the other for the code. If you are concerned about preserving backward compatibility with mod_perl 1.0, or are just experimenting with mod_perl 2.0 while continuing to run mod_perl 1.0 on your production server, simply enable the code-compatibility layer by adding:

use Apache2;
use Apache::compat;

at the top of your startup file. Backward compatibility of the configuration is enabled by default.