code: @Override
  	public LessSource relativeSource(String resource) throws StringSourceException {
  
  		String result = null;
  		if (!resource.startsWith("/")) { // relative URL
  			resource = PathNormalizer.concatWebPath(getName(), resource);
  		}
  		try (Reader rd = getResourceReader(resource)) {
  			result = IOUtils.toString(rd);
  			FilePathMapping linkedResource = FilePathMappingUtils.buildFilePathMapping(resource, rsReaderHandler);
  			if (linkedResource != null) {
  				addLinkedResource(linkedResource);
  				if (bundle != null) {
  					bundle.getFilePathMappings().add(
  							new FilePathMapping(bundle, linkedResource.getPath(), linkedResource.getLastModified()));
  				}
  			}
  
  		} catch (ResourceNotFoundException | IOException e) {
  			throw new BundlingProcessException(e);
  		}
  
  		return new JawrLessSource(bundle, result, resource, this, rsReaderHandler);
  	}
docs: /*
  (non-Javadoc)
  
  @see
  com.github.sommeri.less4j.LessSource.StringSource#relativeSource(java.
  lang.String)