A quirk in the way the Apple Watch handles email content allows users with a little HTML knowledge to include “hidden” versions of email messages that are only visible on the Apple Watch.
Discovered by Dan Foody, a user of email testing, preview and analytics service Litmus, the Apple Watch-specific email scheme takes advantage of an idiosyncrasy in Apple’s solution for delivering and displaying HTML.
Litmus explains that the Apple Watch only displays the plain text portion of an email, ignoring things like remote images in an effort to conserve processing cycles. Email content is first translated from HTML to rich text by the paired iPhone before being sent to the Watch for display.
“Emails usually contain both HTML and plain text elements with Content-Type designations text/html andtext/plain, respectively. With Watch, Apple implements a fallback — text/watch-html — for purposes of replacing complex HTML content. Including an unsuitable HTML element, like a remote image, will force Apple Watch to fall back to plain text and the suitable Content-Type text/html-watch, which results in a rich text-like formatting completely transparent to readers on other devices.”
One thing to keep in mind is that only a handful of email service providers support HTML delivery. If you’d like to try out the feature, you can visit PutsMail, Litmus’ Web-based email testing and debugging tool, which capable of delivering inline plain text, HTML and Watch HTML.
For more information, visit the Litmus website.