Alter widget forms for a specific widget provided by another module.
Modules can implement hook_field_widget_WIDGET_TYPE_form_alter() to modify a specific widget form, rather than using hook_field_widget_form_alter() and checking the widget type.
$element: The field widget form element as constructed by hook_field_widget_form().
$form_state: An associative array containing the current state of the form.
$context: An associative array containing the following key-value pairs, matching the arguments received by hook_field_widget_form():
hook_field_widget_form_alter()
function hook_field_widget_WIDGET_TYPE_form_alter(&$element, &$form_state, $context) {
// Code here will only act on widgets of type WIDGET_TYPE. For example,
// hook_field_widget_mymodule_autocomplete_form_alter() will only act on
// widgets of type 'mymodule_autocomplete'.
$element['#autocomplete_path'] = 'mymodule/autocomplete_path';
}