docs(#500): generalise _ to ancestors (#535)

Author: jimbxb

WYBE.md

@@ -329,9 +329,10 @@ Sometimes you may wish to specify which module the procedure *name* exists in.
 You can further specify which module the procedure *name* is from by preceding
 *name* with a `.` separated module specification, such as *parent*`.`*mod*`.`*name*.
 
-As a convenience, if the first module name in a module specification is `_`, the
-`_` is equivalent to the current module. For example in a module named `foo`,
-`_.`*name* is equivalent to `foo.`*name*
+As a convenience, if the leading module names in a module specification are `_`, the
+series of `_` are equivalent to a prefix of the current module. For example in a 
+module named `foo.bar`, `_.`*name* is equivalent to `foo.bar.`*name*, and `_._`*name* 
+is equivalent to `foo.`*name*.
 
 A procedure call must be preceded by an exclamation point (`!`) if it uses any
 resources, as described in the section on