Clarify CODEOWNERS syntax exceptions (#1551)

* Fix #1407

Say that a CODEOWNERS file follows most, but not all, gitignore syntax rules

* More updates

See #1407 (comment)

* Fix link syntax

oops!

* Update content/github/creating-cloning-and-archiving-repositories/about-code-owners.md

Co-authored-by: hubwriter <hubwriter@github.com>

Co-authored-by: hubwriter <hubwriter@github.com>

Author: ajsirota

content/github/creating-cloning-and-archiving-repositories/about-code-owners.md

@@ -39,9 +39,9 @@ For code owners to receive review requests, the CODEOWNERS file must be on the b
 
 ### CODEOWNERS syntax
 
-A CODEOWNERS file uses a pattern that follows the same rules used in [gitignore](https://git-scm.com/docs/gitignore#_pattern_format) files. The pattern is followed by one or more {% data variables.product.prodname_dotcom %} usernames or team names using the standard `@username` or `@org/team-name` format. You can also refer to a user by an email address that has been added to their {% data variables.product.product_name %} account, for example `user@example.com`.
+A CODEOWNERS file uses a pattern that follows most of the same rules used in [gitignore](https://git-scm.com/docs/gitignore#_pattern_format) files, with [some exceptions](#syntax-exceptions). The pattern is followed by one or more {% data variables.product.prodname_dotcom %} usernames or team names using the standard `@username` or `@org/team-name` format. You can also refer to a user by an email address that has been added to their {% data variables.product.product_name %} account, for example `user@example.com`.
 
-If any line in your CODEOWNERS file contains invalid syntax, the file will not be detected and will not be used to request reviews. Invalid syntax includes inline comments and user or team names that do not exist on {% data variables.product.product_name %}.
+If any line in your CODEOWNERS file contains invalid syntax, the file will not be detected and will not be used to request reviews.
 #### Example of a CODEOWNERS file
 ```
 # This is a comment.
@@ -83,6 +83,13 @@ apps/ @octocat
 # subdirectories.
 /docs/ @doctocat
 ```
+#### Syntax exceptions
+There are some syntax rules for gitignore files that do not work in CODEOWNERS files:
+- Escaping a pattern starting with `#` using `\` so it is treated as a pattern and not a comment
+- Using `!` to negate a pattern
+- Using `[ ]` to define a character range
+
+
 
 ### Further reading