Polymer 如何获取聚合物自定义元素的内部域？

我有一个聚合物自定义元素，如下所示

<custom-element>
  <img src="path1">
  <img src="path2">
  <img src="path3">
  <img src="path4">
</custom-element>

上面的代码在单个div中生成所有图像，即

图像包装器

，如下所示

<div class="image-wrapper">
  <img src="path1">
  <img src="path2">
  <img src="path3">
  <img src="path4">
</div>

<div class="image-wrapper">
  <img src="path1">
</div>
<div class="image-wrapper">
  <img src="path2">
</div>
<div class="image-wrapper">
  <img src="path3">
</div>
<div class="image-wrapper">
  <img src="path4">
</div>

我怎样才能做到这一点呢？

作为一个快速的回答

<custom-element>
  <img src="path1">
</custom-element>
<custom-element>
  <img src="path2">
</custom-element>
<custom-element>
  <img src="path3">
</custom-element>
<custom-element>
  <img src="path4">
</custom-element>

<custom-element>
  <img src="path1">
</custom-element>
<custom-element>
  <img src="path2">
</custom-element>
<custom-element>
  <img src="path3">
</custom-element>
<custom-element>
  <img src="path4">
</custom-element>

<template is="dom-repeat" items="[[paths]]" as="path">
    <custom-element>
      <img src="[[path]]">
    </custom-element>
</template>

paths = [
    "path1",
    "path2",
    "path3",
    "path4",
];