我需要拖放svg元素（路径），但只能在可用区域（rect）内部。我怎么能这样做？
<svg xmlns="http://www.w3.org/2000/svg"
xmlns:xlink="http://www.w3.org/1999/xlink" app-context="doc-2d" x="0px"
y="0px" width="600px" height="900px">
<rect transform="matrix(1,0,0,1,115.04612731933594,153.07086181640625)" width="357.52980041503906" height="482.1732177734375" fill="rgba(255,255,255,1)" stroke="#000000" stroke-width="2.11" stroke-linecap="butt" stroke-linejoin="miter" opacity="1"></rect>
<path id="drag-element" fill="url(#__1521276821859__)" stroke="rgba(201,122,122,1)" stroke-width="14" stroke-linecap="butt" stroke-linejoin="miter" opacity="1" d="M 190.48818969726562 337.8492736816406 L 228.7559051513672 236.16647338867188 L 330.4386901855469 270.06072998046875 L 390.57366943359375 368.46343994140625 L 254.9966278076172 446.09222412109375 L 190.48818969726562 337.8492736816406 Z" transform="translate(-15, 1)"></path>
</svg>