+ * Opens a package file by name. First, local packages are searched for a
+ * match. If a local match is found, the global search path is never
+ * consulted. If no local match is found, the directories in the global search
+ * path are examined, in order.
+ *
+ * When searching the global search path, the first file found which both
+ * matches the given name and can be opened successfully is used. A file
+ * foo.EXT matches the name if foo is equal to name (without regard to case)
+ * and EXT is one of u, utx, uax, umx or unr. If multiple extensions
+ * are valid, they are tried in this order.
+ *
+ * Note that the particular file extension used does not make any difference
+ * as to what sort of objects can be contained in a package.
+ *
+ * Returns the opened package on success, or NULL on failure.