code: func Prefix(prefix string, p AssetPipeline) AssetPipeline {
  	if prefix == "" {
  		return p
  	}
  
  	return &prefixPipeline{
  		prefix:        prefix,
  		AssetPipeline: p,
  	}
  }
docs: // Prefix returns an AssetPipeline that prefixes URLs with the
  // given string