Experimentally, I’ve discovered that you can provide:
- Single line breaks are ignored; double line breaks open a new paragraph.
- Single line breaks can be enforced by ending a line with two spaces (similar to Markdown).
- A limited set of HTML tags (optionally nested), specifically:
<b>…</b>
for boldface,<i>…</i>
for italics,<u>…</u>
for underline,<br />
to enforce a single line break,- I could not find any way to get strikethrough working (neither HTML or Markdown style).
- A fully-formatted URL such as
http://google.com
; this appears as a hyperlink.
(Beware that trying to use an HTML<a>
tag for a custom description does not work and breaks the formatting.) - HTML character entities are supported, such as
→
(→),™
(™) and®
(®); consult this W3 reference for the exhaustive list. - UTF-8 encoded characters are supported, such as é, €, £, ‘, ’, ★ and ☆.
- Indentation isn’t strictly possible, but using a bullet and em space character looks reasonable (
• 
yields “• ”). - Emoji are also supported (though on the website depends on the user’s OS & browser).
Special notes concerning only Google Play app:
- Some HTML tags only work in the app:
<blockquote>…</blockquote>
to indent a paragraph of text,<small>…</small>
for slightly smaller text,<big>…</big>
for slightly larger text,<sup>…</sup>
and<sub>…</sub>
for super- and subscripts.<font color="#a32345">…</font>
for setting font colors in HEX code.
- Some symbols do not appear correctly, such as ‣.
- All these notes also apply to the app’s “What’s New” section.
Special notes concerning only Google Play website:
- All HTML formatting appears as plain text in the website’s “What’s New” section (i.e. users will see the HTML source).