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1. Upload small-caps.php to the /wp-content/plugins/ folder.
2. Activate the plugin through the 'Plugins' menu in WordPress.
3. Add the following styling to your style.css file:

abbr { text-transform:lowercase; font-variant:small-caps }

Optional: If you prefer this to be automatically added to the header of your template, across the themes without editing them yourself manually to add the above styling, then, you may uncomment lines 32 through to 38 in the plugin file small-caps.php .