为什么陆龟会默认隐藏一些修改?

我在源代码中看到了以下内容: http://bitbucket.org/tortoisehg/stable/src/9d917274ab7e/tortoisehg/hgtk/history.py

class FilterBar(gtklib.SlimToolbar):
    'Filter Toolbar for repository log'

    def __init__(self, tooltips, filter_mode, branch_names, repo):
        gtklib.SlimToolbar.__init__(self, tooltips)
        self.filter_mode = filter_mode
        self.buttons = {}
        self.handlers = {}

        self.all = gtk.RadioButton(None, _('All'))
        self.all.set_active(True)
        self.append_widget(self.all, padding=0)
        self.buttons['all'] = self.all