func t_meta_default(key string, dft interface{}, pg *page.Page) interface{} {
	if pg != nil {
		if v := pg.Meta(key); v != nil {
			return v
		}
	}
	return dft
}

func (ctx *context) put_page(uri string, pg *page.Page) {
	if pg != nil {
		if err := ctx.app.pages.Put(uri, pg.GetData()); err != nil {
			ctx.Warn("context put (%s) page failed:(%s)", uri, err)
		}
		if err := ctx.app.pageIndexes.IndexIfNotExist(uri, pg.GetData()); err != nil {
			ctx.Warn("context index (%s) page failed:(%s)", uri, err)
		}
	}
}

func t_tag_class(class string, pg *page.Page) []*html.Node {
	if pg != nil {
		return pg.TagClassAll(class)
	}
	return nil
}

func t_tag_id(id string, pg *page.Page) []*html.Node {
	if pg != nil {
		return pg.TagIDAll(id)
	}
	return nil
}

func t_tag(name string, pg *page.Page) []*html.Node {
	if pg != nil {
		return pg.TagNameAll(name)
	}
	return nil
}

func t_markdown(pg *page.Page) template.HTML {
	if pg != nil {
		return template.HTML(pg.Markdown())
	}
	return template.HTML("")
}

func t_modify_datetime(pg *page.Page) time.Time {
	if pg != nil {
		return pg.ModifyDatetime()
	}
	return time.Time{}
}

func t_meta(key string, pg *page.Page) interface{} {
	if pg != nil {
		return pg.Meta(key)
	}
	return nil
}

func t_uri(pg *page.Page) string {
	if pg != nil {
		return pg.Meta("uri").(string)
	}
	return ""
}

func t_summary(max int, pg *page.Page) string {
	return pg.Summary(max)
}

func t_published_datetime(pg *page.Page) time.Time {
	return pg.PublishedDatetime()
}

func t_title(pg *page.Page) string {
	return pg.Title()
}