This plugin is meant to add the word autocomplete in search input field by using the index includes in Relevanssi database.
So you have to install Relevanssi or version to have it to work..
The JS script used to accomplish the autocompletion work has been developed Lea Verou and is called Awesomplete.
Get Relevanssi Indexed words to have the list.
Upload the folder autocomplete-for-relevanssi to the wp-content plugins directory or install the plugin through WordPress plugins screen directly..
Activate the plugin through 'Plugins screen in WordPress.
Use Settings->Autocomplete for Relevanssi screen to configure the plugin...
But maybe the list displaying feature will be added in version of Autocomplete for Relevanssi.
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