Original hypothetical continuous-value classes
Domain:0 to30 fictional units, both endpoints included.
Low:0 <=value <10
Middle:10 <=value <20
High:20 <=value <=30
Outside domain:finite value <0 or >30
Reject/resolve missing, nonnumeric or nonfinite values before classification.
No real risk/health/business thresholds are asserted.