Select menus are enclosed in parentheses, with each item is enclosed curly
braces.

Example: `1 + 1 = ({one}{+two}{three})`
function(walk) {
        if (!walk.at('({')) return false;
        var endIdx = walk.indexOf('})');
        if (endIdx === null)
          return false;
        // We got a select menu
        walk.skip(2);
        var ctl = this.formCompiler.createCtl('selectMenu');
        ctl.items = [];
        this.out.push('<select');
        this.emitAttrs({
          id: ctl.id,
          name: ctl.id,
          class: ctl.type
        });
        this.out.push('>');
        this.emitMenuItems(ctl, new SubWalker(walk, walk.position, endIdx));
        this.out.push('</select>');
        walk.startFrom(endIdx).skip(2);
        return true;
      }