Field definition in custom field and varchar_ascii When making custom field and doing field definitions for string I came upon this setting.

  'type' =&gt; $field_definition-&gt;getSetting('is_ascii') === TRUE ? 'varchar_ascii' : 'varchar',


I just cant find a reference what would it be if a field definition is set to "varchar_ascii" is it something to do with "Collation" ?
The doc block of database.api.php/Schema API state:


  A special varchar_ascii type is also available for limiting machine name field to US ASCII characters.


You can see its implementation in Schema::createFieldSql() of the MySQL abstraction layer.

So yes, it changes the default UTF-8 character set/collation to ASCII.