It is also possible to remove existing attributes or to add new attributes. +
+Values entered are converted to the right format: for distances, values +may be suffixed with a unit. If the value starts with + or -, it is interpreted +as a relative value; e.g. a -1mm for clearance means "decrease the current +clearance value by 1mm". There are a few fields where negative values are +acceptable, e.g. arc angles; to enforce a negative value (e.g. -90) to +overwrite the angle instead of decreasing it by 90, the # prefix should be used +(i.e. #-90).