There is no function named main() except in the PHP source. In PHP 4.3.0, a new type of error handling in the PHP source (php_error_docref) was introduced. One feature is to provide links to a manual page in PHP error messages when the PHP directives html_errors (on by default) and docref_root (on by default until PHP 4.3.2) are set.
Sometimes error messages refer to a manual page for the function main() which is why this page exists. Please add a user comment below that mentions what PHP function caused the error that linked to main() and it will be fixed and properly documented.
表格 1. Known errors that point to main()