[mkgmap-dev] overlays file

Hi list, looking for rendering some route relations (bycicle, hiking, ecc...) - to be displayed together with the underlying ways - i read somewhere in the list about the _*overlays file*_ within the style files, but unfortunately i cant find anything about it in the wiki , in the help file and in the default style file. could anyone explain to a newbie the usage and the syntax of this file ? could be possibile to get the same result by using the "continue" command in the style-file lines code? (and where can i find some example about it?) Thanx Gianmario.