code: private function needsCompilation($lessPath, $cssPath)
  	{
  		/**
  		 * Checks whether $subject has been modified since $reference was
  		 */
  		$isNewer = function($subject, $reference) {
  			return filemtime($subject) > filemtime($reference);
  		};
  
  		// Check for obvious cases
  		if ($this->forceCompile || !file_exists($lessPath) 
  				|| !file_exists($cssPath) || $isNewer($lessPath, $cssPath))
  		{
  			return true;
  		}
  
  		// Finally, check if any imported file has changed
  		return $this->checkImports($lessPath, $cssPath, $isNewer);
  	}
docs: Checks whether we need to recompile the specified LESS file.
  @param string $lessPath the path to the LESS file
  @param string $cssPath the path to the CSS file it's compiled to
  @return boolean whether we need to recompile it