src/Interval.php
public function setUpper($upper): self
    {
        if ( ! is_numeric($upper)) {
            throw new InvalidArgumentException(
                __METHOD__ . "() expects parameter one, upper, to be a number"
            );    
        }
        
        $this->upper = $upper;
        
        return $this;
    }
public function setUpper($upper): self
    {
        if ( ! is_numeric($upper)) {
            throw new InvalidArgumentException(
                __METHOD__ . "() expects parameter one, upper, to be a number"
            );    
        }
        
        $this->upper = $upper;
        
        return $this;
    }
Sets the interval's upper value

@param   int|float  $upper
@return  self
@throws  InvalidArgumentException  if $upper is not a number
@since   0.1.0