Since Orbeon Forms 4.1, released two weeks ago, the labels and hints for forms you create in Form Builder can be more than just plain text: you can now use HTML in your labels and hints, right from Form Builder. For instance, this allows you to add formatting, as in the example below, where part of the label is in italic, or to add a link to a page with additional information about that field.
By default, labels and hints are just plain text, as this is the most common scenario, and you wouldn't want a less-than sign (<) to be interpreted as the start of an HTML tag. To avoid this, you explicitly enable the HTML mode with a checkbox, which in Form Builder is shown next to labels and hints.