function toFont(options, fallback) {
    options = options || {};
    fallback = fallback || defaults.font;
    let size = valueOrDefault(options.size, fallback.size);
    if (typeof size === 'string') {
        size = parseInt(size, 10);
    }
    let style = valueOrDefault(options.style, fallback.style);
    if (style && !('' + style).match(FONT_STYLE)) {
        console.warn('Invalid font style specified: "' + style + '"');
        style = undefined;
    }
    const font = {
        family: valueOrDefault(options.family, fallback.family),
        lineHeight: toLineHeight(valueOrDefault(options.lineHeight, fallback.lineHeight), size),
        size,
        style,
        weight: valueOrDefault(options.weight, fallback.weight),
        string: ''
    };
    font.string = toFontString(font);
    return font;
}
Parses font options and returns the font object.
@param options - A object that contains font options to be parsed.
@param fallback - A object that contains fallback font options.
@return The font object.
@private