PHPStorm using Strings

hi together,

Here the user is able to type in an integer bigger or equal to 1.

array(
  'name' => __('size','test'),
  'desc' => __('Please give the size from 1(very small) to 10(very big)','test'),
  'id'    => "{$prefix}_room_size",
  'type' => 'number',
  'min'  => 1,
  'step' => 1,
),
 

What would we have to do to only let the user select Strings? E.g.

array(
  'name' => __('size','test'),
  'desc' => __('Please give the size - either samll, middle or big','test'),
  'id'    => "{$prefix}_room_size",
  'type' => 'text',
  'allowedvalues'  => 'small' or 'middle' or 'big',
),