I've found that double-clicking in the expression builder results in varying behavior (possibly due to field names with spaces?)
It would be great if double-clicking a field selected everything from bracket to bracket inclusive, making it simpler to replace one field with another.
For instance:
Current:
IF [AVG AGE] >=5 THEN "Y" ELSE "N" ENDIF
Desired:
IF [AVG AGE] >=5 THEN "Y" ELSE "N" ENDIF