cols

cols
Type:integer
Scope:Display
RenderType:textTable, default

Abstract value for the width of the <textarea> field. To set the textarea to the full width of the form area, use the value 50. Default is 30.

Does not apply to RTE fields.

A simple text editor with 20 width

      'text_4' => [ 
         'exclude' => 1,
         'label' => 'text_4 cols=20, rows=2',
         'config' => [ 
            'type' => 'text',
            'cols' => 20,
            'rows' => 2,
         ],
      ],
      // Example from extension "styleguide", table "tx_styleguide_elements_basic"