coerce(other) {
    switch (other.nodeName) {
      case 'string':
        return other;
      case 'expression':
        return new String(other.nodes.map(function (node) {
          return this.coerce(node).val;
        }, this).join(' '));
      default:
        return new String(other.toString());
    }
  }
Coerce `other` to a string.

@param {Node} other
@return {String}
@api public