17. (11th "Hope Cup" Invitational Competition Question) The function $f(x)$ is defined on $\mathbf{R}$ as an even function with a period of 2. When $x \in [2,3]$, $f(x) = x$. Then, when $x \in [-2,0]$, the analytical expression of $f(x)$ in piecewise function form is , and in a unified form is

保留源文本的换行和格式，直接输出翻译结果如下：

17. (11th "Hope Cup" Invitational Competition Question) The function $f(x)$ is defined on $\mathbf{R}$ as an even function with a period of 2. When $x \in [2,3]$, $f(x) = x$. Then, when $x \in [-2,0]$, the analytical expression of $f(x)$ in piecewise function form is , and in a unified form is
17. Fill $f(x)=\left\{\begin{array}{l}3+(x+1), x+1 \in[-1,0] \\ 3-(x+1), x+1 \in[0,1]\end{array}\right.$ and $f(x)=3-|x+1|, x \in[-2,0]$.

Reason: From the translation and reflection of the graph, it is not difficult to obtain
$f(x)=\left\{\begin{array}{l}x+4, x \in[-2,-1] \\ -x+2, x \in[-1,0] .\end{array}\right.$ This leads to the result.