def font_stretch(keyword):
    """``font-stretch`` descriptor validation."""
    return keyword in (
        'ultra-condensed', 'extra-condensed', 'condensed', 'semi-condensed',
        'normal',
        'semi-expanded', 'expanded', 'extra-expanded', 'ultra-expanded')
``font-stretch`` descriptor validation.
weasyprint/css/validation/descriptors.py