The Hewlett-Packard Raster Transfer Language (HP RTL) is a subset of the #PrinterCommandLanguage (PCL) language. It is used to embed true raster images (bitmaps) into #plotter files. Modern plotters (like HP DesignJets) are raster devices, so they need a raster-based language. For backward compatibility they also support the #HPGL2 (formerly HP-GL) vector language, so the HP RTL language is designed for mixing with the HP-GL/2 language.