HI. I’ve looked at the custom rule editor. OK Expression functions etc etc

*The notes say “Rules should be ordered by specificity. Later rules take precedence over earlier rules;”*

- PLease explain ‘specificity’ in this context.
- order: so the LAST rules are evaluated first ?

example, and it needs to be evaluated in this order where the ‘specificity’ overlaps

take this example for a mix : this is the CLEARANCE rule set for one board I have .

- different differential pairs must have track to track clearance of 0.5mm
- If in polygon and is a top layer polygon , and has footprint ‘xyz’ OR has footprint(‘avc’ then IF same net, clearance >= 0
- If in polygon AND on bottom layer , different nets clearance >= 0.3mm except for vias which is >= 0.25mm
- if in polygon and on top layer AND different net, then clerance >= 0.25mm except if SMT pad, clearance> 0.6mm
- If in polygon and on MID layer and is ANY differential pair, for different nets only, clearance >= 0.4mm
- If in polygon and on MID layer and NET CLASS in MV then for different nets only, clearance to be >=0.5mm
- If in polygon AND on MID layer, and has footprint(‘fff’) and if different net, clearance >=0.5mm
- If in Polygon and on MID layer , and different nets , clearance >=0.3mm
- if NOT in polygon, clearance >- 0.099mm

So, for the example of 5,6,7,8 , clearly 8 is the catch all and needs to be evaaluated if the the match does not occur with 5,6,7.

and the last rule (9) is the catch all- if none of the rules match, the the clearance > 0.099mm .

(what 0.099 ? because altium has precision issues- I think internally it is all 64 bit integer tenth mil)