made semantic_markup unique

  TODO: move this to 'common snippet' to be included in both pages

Author: bcoca

docs/docsite/rst/dev_guide/plugins_documenting.rst

@@ -244,7 +244,7 @@ You can link from your plugin documentation to other module docs, other resource
 
    Because it stands out better, use ``seealso`` for general references over the use of notes or adding links to the description.
 
-.. _semantic_markup:
+.. _plugins_semantic_markup:
 
 Semantic markup within plugin documentation
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