SelfLoader (Perl in a Nutshell, 2nd Edition)

8.184. SelfLoader

Used when you want to include functions in your program but want to load them only if necessary. Functions that will be self-loaded are placed after the line:

_  _DATA_  _

in your program. When the code is compiled, compilation stops at the _ _DATA_ _ token. The SelfLoader exports the AUTOLOAD subroutine to the package; this subroutine loads the subroutines after _ _DATA_ _ when they are require d.