Improve doc for :type-at. (#14780)

docs/users_guide/ghci.rst

@@ -2937,7 +2937,7 @@ commonly used commands.
 	*X> :type +d length
 	length :: [a] -> Int
 
-.. ghci-cmd:: :type-at; ⟨module⟩ ⟨line⟩ ⟨col⟩ ⟨end-line⟩ ⟨end-col⟩ [⟨name⟩]
+.. ghci-cmd:: :type-at; ⟨path⟩ ⟨line⟩ ⟨col⟩ ⟨end-line⟩ ⟨end-col⟩ [⟨name⟩]
 
     Reports the inferred type at the given span/position in the module, e.g.:
 
@@ -2949,6 +2949,13 @@ commonly used commands.
     This command is useful when integrating GHCi with text editors and
     IDEs for providing a show-type-under-point facility.
 
+    The first parameter (path) must be a file path and not a module name.
+    The type of this path is dependent on how the module was loaded into GHCi:
+    If the module was loaded by name, then the path name calculated by GHCi
+    as described in :ref:`ghci-modules-filenames` must be used.
+    If the module was loaded with an absolute or a relative path,
+    then the same path must be specified.
+
     The last string parameter is useful for when the span is out of
     date, i.e. the file changed and the code has moved. In which case
     :ghci-cmd:`:type-at` falls back to a general :ghci-cmd:`:type` like lookup.