This sets an install-time complex search-and-replace function allowing the setting of platform-specific variables in an installed file.
if $type is php-const, then $to must be the name of a PHP Constant. If $type is pear-config, then $to must be the name of a PEAR config variable accessible through a PEAR_Config::get() method. If type is package-info, then $to must be the name of a section from the package.xml file used to install this file.
relative path of file (relative to packagedirectory option)
variable type, either php-const, pear-config or package-info
text to replace in the source file
variable name to use for replacement