_attributes(line) {
        let attrs = '';
        for (let prop in line) {
            attrs += this.pfx;

            if (prop === 'type') {
                attrs += `="${line[prop]}" `
            } else if (prop !== 'value') {
                attrs += `-${prop}="${line[prop]}" `
            }
        }

        return attrs;
    }
Helper function for generating attributes string.

@param {Object} line - Line data object.
@returns {string} - String of attributes.