silverstripe-framework/docs/en/howto/cms-formfield-help-text.md

How to Show Help Text on CMS Form Fields

Sometimes you need to express more context for a form field than is suitable for its <label> element. The CMS provides you with an easy way to transform form field attributes into either help text shown alongside the field, or a tooltip which shows on demand.

The FormField->setDescription() method will add a <span class="description"> at the last position within the field, and expects unescaped HTML content.

:::php
TextField::create('MyText', 'My Text Label')
	->setDescription('More <strong>detailed</strong> help');

To show the help text as a tooltip instead of inline, add a .cms-description-tooltip class.

:::php
TextField::create('MyText', 'My Text Label')
	->setDescription('More <strong>detailed</strong> help')
	->addExtraClass('cms-help-tooltip');

Tooltips are only supported for native, focusable input elements, which excludes more complex fields like GridField, UploadField or DropdownField with the chosen.js behaviour applied.

Note: For more advanced help text we recommend using Custom form field templates;