Macro with matches

Hi, I was trying to define some macros using the matches operator but I get not result, just a error of the macro definition. After reading the wireshark doc I get no error with that example but what I want to set is something like:

tcp matches "([x90])\1{$1,}" --> this would find $1 times the x90 opcode. I've called this macro BO and I've tried the following without success.:

${BO:100} $BO{100}

The problem is not the matches operator because this work --> tcp matches "$1". So, for some reason the macro doesn't work when you use hex digit

Any ideas? Thank you in advance