, ["top", "left"], true)) {
                return 0;
            } elseif (\in_array($value, ["bottom", "right"], true)) {
                return "100%";
            } else {
                return $value;
            }
        }, $values);

        if (!isset($values[1])) {
            $values[1] = $values[0];
        }

        return $values;
    }

    /**
     * @param string $val
     * @return string|null
     */
    protected function parse_image_resolution(string $val): ?string
    {
        // If exif data could be get:
        // $re = '/^\s*(\d+|normal|auto)(?:\s*,\s*(\d+|normal))?\s*$/';

        $re = '/^\s*(\d+|normal|auto)\s*$/';

        if (!preg_match($re, $val, $matches)) {
            return null;
        }

        return $matches[1];
    }

    /**
     * auto | normal | dpi
     */
    protected function _compute_background_image_resolution(string $val)
    {
        return $this->parse_image_resolution($val);
    }

    /**
     * auto | normal | dpi
     */
    protected function _compute_image_resolution(string $val)
    {
        return $this->parse_image_resolution($val);
    }

    /**
     * @link https://www.w3.org/TR/css-break-3/#propdef-orphans
     */
    protected function _compute_orphans(string $val)
    {
        return $this->compute_integer($val);
    }

    /**
     * @link https://www.w3.org/TR/css-break-3/#propdef-widows
     */
    protected function _compute_widows(string $val)
    {
        return $this->compute_integer($val);
    }

    /**
     * @link https://www.w3.org/TR/css-color-4/#propdef-opacity
     */
    protected function _compute_opacity(string $val)
    {
        $number = self::CSS_NUMBER;
        $pattern = "/^($number)(%?)$/";

        if (!preg_match($pattern, $val, $matches)) {
            return null;
        }

        $v = (float) $matches[1];
        $percent = $matches[2] === "%";
        $opacity = $percent ? ($v / 100) : $v;

        return max(0.0, min($opacity, 1.0));
    }

    /**
     * @link https://www.w3.org/TR/CSS21//visuren.html#propdef-z-index
     */
    protected function _compute_z_index(string $val)
    {
        if ($val === "auto") {
            return $val;
        }

        return $this->compute_integer($val);
    }

    /**
     * @param FontMetrics $fontMetrics
     * @return $this
     */
    public function setFontMetrics(FontMetrics $fontMetrics)
    {
        $this->fontMetrics = $fontMetrics;
        return $this;
    }

    /**
     * @return FontMetrics
     */
    public function getFontMetrics()
    {
        return $this->fontMetrics;
    }

    /**
     * Generate a string representation of the Style
     *
     * This dumps the entire property array into a string via print_r.  Useful
     * for debugging.
     *
     * @return string
     */
    /*DEBUGCSS print: see below additional debugging util*/
    public function __toString(): string
    {
        $parent_font_size = $this->parent_style
            ? $this->parent_style->font_size
            : self::$default_font_size;

        return print_r(array_merge(["parent_font_size" => $parent_font_size],
            $this->_props), true);
    }

    /*DEBUGCSS*/
    public function debug_print(): void
    {
        $parent_font_size = $this->parent_style
            ? $this->parent_style->font_size
            : self::$default_font_size;

        print "    parent_font_size:" . $parent_font_size . ";\n";
        print "    Props [\n";
        print "      specified [\n";
        foreach ($this->_props as $prop => $val) {
            print '        ' . $prop . ': ' . preg_replace("/\r\n/", ' ', print_r($val, true));
            if (isset($this->_important_props[$prop])) {
                print ' !important';
            }
            print ";\n";
        }
        print "      ]\n";
        print "      computed [\n";
        foreach ($this->_props_computed as $prop => $val) {
            print '        ' . $prop . ': ' . preg_replace("/\r\n/", ' ', print_r($val, true));
            print ";\n";
        }
        print "      ]\n";
        print "      cached [\n";
        foreach ($this->_props_used as $prop => $val) {
            print '        ' . $prop . ': ' . preg_replace("/\r\n/", ' ', print_r($val, true));
            print ";\n";
        }
        print "      ]\n";
        print "    ]\n";
    }
}