Builds a UNIX-style path from the base path and absolute or relative path inputs.
A UNIX-style path uses the slash (/) character between path segments. An absolute path begins with a slash.
base path is the path to which the VI appends the absolute or relative path input if that path is relative.
absolute or relative path is the path that the VI converts to a UNIX-style path. If the path is relative, the VI appends to the base path. If the path is absolute, the VI uses it alone.