TKpathname returns variations of a full file pathname to a specified stack. It can simply return the full pathname, leafname (just the filename), volume name, or the full pathname with an "added" filename.
TKpathname is a powerful XFCN and its use is not always obvious. For instance, it can be used to add a stack to the "stacksinuse" hierarchy in HyperCard or set up a root file path for the creation of new stacks in another folder.