Text Based Content Search Based On Tagging
Out of the box Sitecore offers Content Editors the power to create tags, and assign them to content items using the Tagging field in standard values.
Tagging Standard Value>
When analysing the indexes using LUKE, you can see that Sitecore indexes the ID's of each tag. This makes it difficult to perform a text based content search that also matches on tags.
Luke Index View
However Sitecore gives us the power to create computed fields in search indexes. This means we can create new fields within the index and programmatically create text into the index.
This example below uses a computed field that instead of indexing the ID of the tag, instead adds the item name of each tag seperated by a space. This then allows you to perform a text based search against the tag. (Sitecore by default indexes the __Semantics field, so here i'm creating a new field in the index called "tags" not to override any standard Sitecore functionality)
Computed Field Class
Add this XML to the "AddComputedIndexField" section of your search index config.