silverstripe-frameworktest/code/GridFieldTestPage.php

<?php
class GridFieldTestPage extends TestPage
{

    private static $has_one = array(
        "HasOneCompany" => "Company",
    );

    private static $has_many = array(
        "HasManyCompanies" => "Company",
    );

    private static $many_many = array(
        "ManyManyCompanies" => "Company",
    );
    
    public function getCMSFields()
    {
        $fields = parent::getCMSFields();

        $grids = array();

        $config = new GridFieldConfig_RecordEditor();
        $grid = new GridField('Companies', 'Companies', new DataList('Company'), $config);
        $fields->addFieldToTab('Root.NoRelation', $grid);
        $grids[] = $grid;

        $config = new GridFieldConfig_RelationEditor();
        $grid = new GridField('HasManyCompanies', 'HasManyCompanies', $this->HasManyCompanies(), $config);
        $fields->addFieldToTab('Root.HasMany', $grid);
        $grids[] = $grid;

        $config = new GridFieldConfig_RelationEditor();
        $grid = new GridField('ManyManyCompanies', 'ManyManyCompanies', $this->ManyManyCompanies(), $config);
        $fields->addFieldToTab('Root.ManyMany', $grid);
        $grids[] = $grid;

        foreach ($grids as $grid) {
            $grid
                ->setDescription('This is <strong>bold</strong> help text');
                // ->addExtraClass('cms-description-tooltip');
        }

        return $fields;
    }
}

class GridFieldTestPage_Controller extends Page_Controller
{

    private static $allowed_actions = array(
        'Form',
    );
    
    /**
     *
     * @var string
     */
    public $Title = "GridFieldTestPage";
    
    public function init()
    {
        parent::init();
        Requirements::css('frameworktest/css/gridfieldtest.css', 'screen');
    }
    
    /**
     *
     * @return Form 
     */
    public function Form()
    {
        $config = new GridFieldConfig_RecordEditor();
        
        $grid = new GridField('Companies', 'Companies', new DataList('Company'), $config);
        return new Form($this, 'Form', new FieldList($grid), new FieldList());
    }
}