I am using the dropdown component from the Element UI library in Vue. The documentation can be found here:

I have already set placement="top" on the el-dropdown.

The dropdown appears at the above of the element as expected. However, sometimes I notice that the dropdown appears below the element, even when there is enough space above to display it.

I would like to ask: what conditions does Element UI use to determine whether the dropdown appears above or below the element? Do we have any way to fixed it always show on top?