function onChange( event ) {
		var err;
		if ( event === 'rename' ) {
			if ( self._watcher ) {
				debug( 'Encountered a "rename" event for the source presentation file.' );
				err = new Error( 'unexpected error. Encountered a "rename" event for the source presentation file. No longer watching source presentation file for changes.' );
				self.unwatch( err );
			}
			return;
		}
		// Case: event === 'change'
		debug( 'Detected a change to the source presentation file.' );
		self.reload();
		self.emit( 'change' );
	}
Callback invoked upon a modification to a presentation source file.

@private
@param {string} event - event type
@param {(string|Buffer)} filename - name of file which triggered the event
@returns {void}