Postulate that snippet tags be closed

CHANGELOG.md

@@ -56,6 +56,10 @@ This is the change log for the REUSE Specification.
 
 ### Fixed
 
+- Clarified that snippet tags must be closed. This was technically already the
+  case with a certain reading of the SPDX specification, but it has now been
+  made explicit.
+
 ### Security
 
 ## 3.2 - 2024-07-03

site/content/en/spec-3.3.md

@@ -177,12 +177,15 @@ An example of a comment header:
 #### In-line Snippet comments
 
 Sometimes Licensing Information only applies to a certain Snippet instead of the
-whole Commentable File. For these cases SPDX snippet tags MUST be used for that
-Snippet (as defined in [SPDX Specification, Annex
+whole Commentable File. You SHOULD use SPDX snippets to license these Snippets.
+When implementing SPDX snippets, you MUST use SPDX snippet tags (as defined in
+[SPDX Specification, Annex
 H](https://spdx.github.io/spdx-spec/v2.3/file-tags/#h3-snippet-tags-format)).
 This means that Copyright Notices inside of Snippets MUST be prefixed with
 `SPDX-SnippetCopyrightText`.
 
+Each Snippet that is opened MUST be closed with `SPDX-SnippetEnd`.
+
 Like with comment headers, the SPDX snippet tags SHOULD be commented.
 
 A Snippet SHOULD contain both a Copyright Notice and an SPDX License Expression.