maptools, filename writing shapefiles

says (p. 6): "All file names adhere to the 8.3 naming convention. The main
file, the index file, and the dBASE file have the same prefix. The prefix
must start with an alphanumeric character (aZ, 09), followed by zero or up
to seven characters (aZ, 09, _, -). The suffix for the main file is .shp.
The suffix for the index file is .shx. The suffix for the dBASE table is
.dbf."

So, the number of characters was the trouble origin (... up to 7 
characters). Easy to manage when known. This also means that ESRI 
ArcGISdoes not itself comply to the standard since one can use much more 
than 7 characters naming shapefiles from there....

Thanks a lot for maptools (those fonctions to write shapefiles are really 
useful) and the clarification.

All the best,

Patrick