Many of the rescanning lines in the Wave trace output for a macro I am tracing show either just a single underscore ( _ ), where the output is empty, or a number and and underscore ( 1_ ) where it is actually just the number which is being output. What is the reason for the underscore ?

IIRC, the _ is used as a (readable) representation for the (empty) placeholder token, which disappears from the final output, but is helpful for debugging purposes. Regards Hartmut --------------- http://boost-spirit.com