Rewrite -# docs

docs/command-line.md

@@ -507,10 +507,13 @@ start of the first section.</br>
 ## Filenames as tags
 <pre>-#, --filenames-as-tags</pre>
 
-When this option is used then every test is given an additional tag which is formed of the unqualified
-filename it is found in, with any extension stripped, prefixed with the `#` character.
+This option adds an extra tag to all test cases. The tag is `#` followed
+by the unqualified filename the test case is defined in, with the _last_
+extension stripped out.
+
+For example, tests within the file `tests\SelfTest\UsageTests\BDD.tests.cpp`
+will be given the `[#BDD.tests]` tag.
 
-So, for example,  tests within the file `~\Dev\MyProject\Ferrets.cpp` would be tagged `[#Ferrets]`.
 
 <a id="colour-mode"></a>
 ## Override output colouring

docs/test-cases-and-sections.md

@@ -69,7 +69,8 @@ All tag names beginning with non-alphanumeric characters are reserved by Catch.
 
 * `[!nonportable]` - Indicates that behaviour may vary between platforms or compilers.
 
-* `[#<filename>]` - running with `-#` or `--filenames-as-tags` causes Catch to add the filename, prefixed with `#` (and with any extension stripped), as a tag to all contained tests, e.g. tests in testfile.cpp would all be tagged `[#testfile]`.
+* `[#<filename>]` - these tags are added to test cases when you run Catch2
+                    with [`-#` or `--filenames-as-tags`](command-line.md#filenames-as-tags).
 
 * `[@<alias>]` - tag aliases all begin with `@` (see below).