code: function getValue(ckey, expr) {
  
      if (ckey !== 'if') {
        var yes = expr in cc.varset ? 1 : 0
        return ckey === 'ifdef' ? yes : yes ^ 1
      }
  
      // returns the raw value of the expression
      return evalExpr(expr, cc.varset, emitError)
    }
docs: Expression evaluation. Intercepts the `#ifdef/ifndef` shorthands, call `evalExpr` for `#if` statements.