code: function(hoast, files) {
  		debug(`Running module.`);
  		
  		// Loop through the files.
  		const filtered = files.filter(function(file) {
  			debug(`Filtering file '${file.path}'.`);
  			
  			// If it does not match
  			if (this.expressions && hoast.helpers.matchExpressions(file.path, this.expressions, options.patternOptions.all)) {
  				debug(`File path valid for skipping.`);
  				return true;
  			}
  			
  			// If it is in the list and not changed since the last time do not process.
  			if (this.list[file.path] && this.list[file.path] >= file.stats.mtimeMs) {
  				debug(`File not changed since last process.`);
  				return false;
  			}
  			
  			debug(`File changed or not processed before.`);
  			// Update changed time and process.
  			this.list[file.path] = file.stats.mtimeMs;
  			return true;
  		}, mod);
  		debug(`Finished filtering files.`);
  		
  		// Return filtered files.
  		return filtered;
  	}
docs: Main module method.