Simplify

Author: Colin Robertson

docs/build/reference/external-external-headers-diagnostics.md

@@ -159,7 +159,7 @@ With this change to the library header, the author of the library ensures that t
 
 ### `system_header` pragma
 
-`#pragma system_header` is an intrusive header marker that allows library writers to mark certain headers as external. A header file containing `#pragma system_header` is considered external from the point of the pragma onward, exactly as if it was in a directory that was specified as external on the command line. The compiler emits any diagnostics after the marker at the warning level specified by **`/external:Wn`**. For more information, see [`system_header` pragma](../../preprocessor/system-header-pragma.md).
+`#pragma system_header` is an intrusive marker that allows library writers to mark certain headers as external. A file containing `#pragma system_header` is considered external from the point of the pragma to the end of the file, as if it were specified as external on the command line. The compiler emits any diagnostics after the pragma at the warning level specified by **`/external:Wn`**. For more information, see [`system_header` pragma](../../preprocessor/system-header-pragma.md).
 
 ### Limitations