getRootFileSystem
Retrieves the relative path to the root of the file system. The root of the file system is determined by the working directory of the current subdocument.
Example:
When used in the root folder: returns
.When used in
<root>/subfolder: returns..When used in
<root>/subfolder1/subfolder2: returns../..
Return
a string value of the relative path to the root of the file system
Throws
if the relative path cannot be determined