If I perform a rmname operation on an element in a parent stream does this also delete the element in the child stream?
No.
rmname will create an new version of the parent directory of the element you are removing.
That new version of the parent directory will no longer reference that element, and that new version will be created in the parent stream associated branch.
That has nothing to do with the versions of that same directory created in the child stream associated branch.
Those versions still reference that element.
来源：https://stackoverflow.com/questions/8717359/does-rmname-on-parent-stream-remove-element-from-child-stream