Use: callstack(0x80000000).
!callstack(value) works as a 'does not contain'.
Add strings to expr.h conditionals.
Use quotations: callstack("anim") to check symbols/name.
This is necessary to retain precision above 32 bits, but more importantly to prevent an expression like (0x80000000 | 1) from flipping the sign of the result.
Martino Fontana