predefined boolean constant.
is a synonym of the constant value zero (0)
that is useful in expressions.
If it is used stand-alone as a condition statement (see
condition(4)) it will block system execution, as if it were a
This keyword is not supported in Spin versions prior to 3.0.
Because it is intercepted in the lexical analyzer as a meta-term,
it shows up in traces as its numeric equivalent
skip(1), true(1), condition(4).