Dev HOWTO: Add a new meta tag to an existing module, suitable for a patch

Drupal 7

At a rudimentary level:

• Decide whether the new meta tags should go in the main module or a submodule,
• Edit that module's "*.metatag.inc" file,
• Scroll down to the hook_metatag_info() implementation,
• Duplicate some of the $info['tags'] variables
• Tweak the variable accordingly. note that the array key, .e.g. the 'robots' part of $info['tags']['robots'], is what defines the meta tag's name.
• Upload the patch and collaborate with others in the community to make sure it works as intended.

An example of inherited meta tag addition:

• Adding Meta Tags to Drupal Content: https://www.ostraining.com/blog/drupal/meta-tags/

Drupal 8

There are several steps necessary to create a new meta tag in Drupal 8:

• Create a new plugin file with the appropriate structure.
• Add lines in the config/schema/[MODULENAME].metatag_tag.schema.yml file
• Add the meta tag to the src/Tests/[MODULENAME]TagsTest.php file in the $tags array.