富文本物料不支持

物料通过contentEditable实现富文本编辑，发现如果init传参designMode不设置为live，则contentEditable无法输入内容，而设置为live则无法拖拽、删除物料。有两个疑问想请教：

1. designMode为live具体的作用是什么？这个在文档里未找到
2. 为何不能直接支持contentEditable元素的编辑呢？主要考虑是什么

Start by reproducing the reported behavior with the init designMode option and a contentEditable material. Compare editing when designMode is not live with dragging and deletion when it is live, then determine the intended behavior and document or scope the required support; the issue names no files or tests.

Written by the indexing model from the issue text.