code/models/editablefields/EditableFieldLiteral.php
public function getFieldConfiguration()
    {
        $customSettings = unserialize($this->CustomSettings);
        $content        = (isset($customSettings['Content'])) ? $customSettings['Content'] : '';
        $textAreaField  = new TextareaField(
            $this->getSettingName('Content'), 'HTML', $content
        );
        $textAreaField->setRows(4);
        $textAreaField->setColumns(20);

        return [
            $textAreaField,
        ];
    }
public function getFieldConfiguration()
    {
        $customSettings = unserialize($this->CustomSettings);
        $content        = (isset($customSettings['Content'])) ? $customSettings['Content'] : '';
        $textAreaField  = new TextareaField(
            $this->getSettingName('Content'), 'HTML', $content
        );
        $textAreaField->setRows(4);
        $textAreaField->setColumns(20);

        return [
            $textAreaField,
        ];
    }
Get extra configuration fields.

@return array