About Expressions Output   What you should see What you should not see 01 No expression About Expressions A A and B A and B and C A and C B C A and B and C and D     02 Not A About Expressions B C A A and B A and B and C A and C A and B and C and D Any topic with the tag A   03 Not B About Expressions A A and C C   A and B A and B and C B A and B and C and D Any topic with the tag B   04 Not C About Expressions A A and B B     A and B and C A and C C A and B and C and D Any topic with the tag C   05 Not A AND Not B About Expressions C A A and B A and B and C A and C B A and B and C and D These topics have one OR more of the tags and are excluded.   06 Not A AND Not C About Expressions B   A A and B A and B and C A and C C A and B and C and D These topics have one OR more of the tags and are excluded.   07 Not A AND Not B AND Not C About Expressions   A A and B A and B and C A and C B C A and B and C and D These topics have one OR more of the tags and are excluded.   08 Not A OR Not B About Expressions A A and C B C   A and B A and B and C A and B and C and D These topics have tags A AND B applied and are excluded 09 Not A OR Not C About Expressions A A and B B C   A and B and C A and C A and B and C and D These topics have tags A AND C applied and are excluded 10 Not A OR Not B OR Not C About Expressions A A and B A and C B C   A and B and C A and B and C and D These topics have tags A AND B AND C applied and are excluded   As can be seen, the AND/OR in the expression is reversed in what you see. This was less obvious in Classic version as can be seen by looking at Expression 05.   If written using the Advanced mode, it shows Not A and Not B. You would expect that to mean a topic would have to have both those tags applied to be excluded.       If viewed in Basic mode however, it is less clear. Everyone assumed that either tag would exclude the topic but as shown above, that wasn't how the code got written behind the scenes.       This dates back to when RoboHelp first added tags and expressions way before Adobe's ownership. The problem now is that to reverse that would wreck all existing expressions!