defunkt/pystache — comment on commit 75254d671adcf0cbc56a9c86cb831d6b5a7676dc
File:  line 0
By lambacck:

If you already have values that are escaped by markupsafe then they don't get double escaped. The use case was providing pre-escaped values that could be used in mustache templates and then using the result of the mustache templates in Mako (Jinja would also work). I was using mustache to allow end users to have "safe" templates for site customization within a larger CMS style system.