constructor(config) {
        super();
        this.config = config;

        // Construct a pattern which matches the rust implementation:
        const digit_pattern = `[^\\d]+|\\d${this.config.individual_digits ? '' : '+'}`;
        this.pattern = new RegExp(digit_pattern, 'gu');
    }
@param {Object} config The configuration options for the pre-tokenizer.
@param {boolean} config.individual_digits Whether to split on individual digits.