* Get the value of property as {@link String}.
     * @param propertyKey The key of the property. (NotNull)
     * @return The value of found property. (NotNull: if not found, exception)
     * @throws ConfigPropertyNotFoundException When the property is not found.
     */
    String get(String propertyKey);

    /**
     * Is the property true?
     * @param propertyKey The key of the property which is boolean type. (NotNull)

$property-class);\n\n    // Use custom CSS variable name if present, otherwise default to `class`\n    $css-variable-name: if(map-has-key($utility, css-variable-name), map-get($utility, css-variable-name), map-get($utility, class));\n\n    // State params to generate pseudo-classes\n    $state: if(map-has-key($utility, state), map-get($utility, state), ());\n\n    $infix: if($property-class == \"\" and str-slice($infix, 1, 1) == \"-\", str-slice($infix, 2), $infix);\n\n    // Don't prefix if value...