See Form Styling for what is/not supported in terms of formatting text. Specifically, in relation to inline html, please note:
Many Markdown implementations support inline HTML, but Collect only supports a small subset of HTML elements. Support of HTML is further limited because:
- Your exact Android device, operating system version, and other device-related factors will affect what HTML can be rendered, and how it is rendered.
- HTML is not supported by other form rendering tools in the XForms ecosystem. For example, HTML elements that work in Collect may not work in Enketo.
For these reasons, we do not recommend using HTML in forms (except the
<span>element noted below).
[emphasis added]
