A handler is a piece of code used to define what a program will do with a specific type of file when it is requested. Most files have implicit handlers based on file type, but if you want a different action to be taken when the file is requested, you need to add an explicit handler.
The server sends any file ending in .asis without adding an HTTP header, so your .asis files must include their own HTTP headers. This handler allows you to attach custom headers to your files without creating special CGI scripts to manage them. Be sure to include a status line.
This Imagemap handler provides a list of directives containing linked image regions so that when a non-graphical browser selects the image, it will provide a list of links available from the image. Optional comments can be included in the map file.
.shtml and .html
This is the "Normal" way to send HTML and graphics files. Files will be sent with HTTP responses, headers and the file's data. Any file not handled by another handler is served by this method. .shtml and .html are Server Parsed documents, or Server Side Includes (SSI).
Further Information on Handlers: